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  • 101. Jovanović, A.
    et al.
    Dobrota, A. S.
    Rafailović, L. D.
    Mentus, S. V.
    Pašti, Igor
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. University of Belgrade, Faculty of Physical Chemistry, Serbia.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; Humboldt University, Germany.
    Skorodumova, Natalia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Structural and electronic properties of V2O5 and their tuning by doping with 3d elements-modelling using the DFT+ U method and dispersion correction2018Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 20, s. 13934-13943Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New electrode materials for alkaline-ion batteries are a timely topic. Among many promising candidates, V2O5 is one of the most interesting cathode materials. While having very high theoretical capacity, in practice, its performance is hindered by its low stability and poor conductivity. As regards the theoretical descriptions of V2O5, common DFT-GGA calculations fail to reproduce both the electronic and crystal structures. While the band gap is underestimated, the interlayer spacing is overestimated as weak dispersion interactions are not properly described within GGA. Here we show that the combination of the DFT+U method and semi-empirical D2 correction can compensate for the drawbacks of the GGA when it comes to the modelling of V2O5. When compared to common PBE calculations, with a modest increase in the computational cost, PBE+U+D2 fully reproduced the experimental band gap of V2O5, while the errors in the lattice parameters are only a few percent. Using the proposed PBE+U+D2 methodology we studied the doping of V2O5 with 3d elements (from Sc to Zn). We show that both the structural and electronic parameters are affected by doping. Most importantly, a significant increase in conductivity is expected upon doping, which is of great importance for the application of V2O5 in metal-ion batteries.

  • 102. Kaewmaraya, Thanayut
    et al.
    Luo, Wei
    Yang, Xiao
    Panigrahi, Puspamitra
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    A new, layered monoclinic phase of Co3O4 at high pressure2015Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 30, s. 19957-19961Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the crystal structures and electronic properties of a Co3O4 spinel under high pressure. Co3O4 undergoes a first-order transition from a cubic (CB) Fd (3) over barm to a lower-symmetry monoclinic (MC) P2(1)/c phase at 35 GPa, occurring after the local high-spin to low-spin phase transition. The high-pressure phase exhibits the octahedral coordination of Co(II) and Co(III), whereas the CB phase contains the fourfold coordination of Co(II) and the sixfold coordination of Co(III). The CB-to-MC transition is attributed to the charge-transfer between the di-and trivalent cations via the enhanced 3d-3d interactions.

  • 103. Kanhere, Pushkar
    et al.
    Shenai, Prathamesh
    Chakraborty, Sudip
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Condense Matter Theory Group, Department of Physics and Astronomy, Uppsala University.
    Zheng, Jianwei
    Chen, Zhong
    Mono- and co-doped NaTaO3 for visible light photocatalysis2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 30, s. 16085-16094Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electronic structures of doped NaTaO3 compounds are of significant interest to visible light photocatalysis. This work involves the study of the band gap, band edge potentials, and thermodynamic stability of certain mono-doped and co-doped NaTaO3 systems, using DFT-PBE as well as hybrid (PBE0) functional calculations. Doping of certain non-magnetic cations (Ti, V, Cu, Zn, W, In, Sn, Sb, Ce, and La), certain anions (N, C, and I), and certain co-dopant pairs (W-Ti, W-Ce, N-I, N-W, La-C, Pb-I, and Cu-Sn) is investigated. Our calculations suggest that substitutional doping of Cu at the Ta site, Cu at the Na site, and C at the O site narrows the band gap of NaTaO3 to 2.3, 2.8, and 2.1 eV, respectively, inducing visible light absorption. Additionally, passivated co-doping of Pb-I and N-W narrows the band gap of NaTaO3 to the visible region, while maintaining the band potentials at favorable positions. Hybrid density of states (DOS) accurately describe the effective band potentials and the location of mid-gap states, which shed light on the possible mechanism of photoexcitation in relation to the photocatalysis reactions. Furthermore, the thermodynamic stability of the doped systems and defect pair binding energies of co-doped systems are discussed in detail. The present results provide useful insights into designing new photocatalysts based on NaTaO3.

  • 104. Kapla, Jon
    et al.
    Engstrom, Olof
    Stevensson, Baltzar
    Wohlert, Jakob
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Widmalm, Goran
    Maliniak, Arnold
    Molecular dynamics simulations and NMR spectroscopy studies of trehalose-lipid bilayer systems2015Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 34, s. 22438-22447Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The disaccharide trehalose (TRH) strongly affects the physical properties of lipid bilayers. We investigate interactions between lipid membranes formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and TRH using NMR spectroscopy and molecular dynamics (MD) computer simulations. We compare dipolar couplings derived from DMPC/TRH trajectories with those determined (i) experimentally in TRH using conventional high-resolution NMR in a weakly ordered solvent (bicelles), and (ii) by solid-state NMR in multilamellar vesicles (MLV) formed by DMPC. Analysis of the experimental and MD-derived couplings in DMPC indicated that the force field used in the simulations reasonably well describes the experimental results with the exception for the glycerol fragment that exhibits significant deviations. The signs of dipolar couplings, not available from the experiments on highly ordered systems, were determined from the trajectory analysis. The crucial step in the analysis of residual dipolar couplings (RDCs) in TRH determined in a bicelle-environment was access to the conformational distributions derived from the MD trajectory. Furthermore, the conformational behavior of TRH, investigated by J-couplings, in the ordered and isotropic phases is essentially identical, indicating that the general assumptions in the analyses of RDCs are well founded.

  • 105.
    Kharkov, Boris B.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Dvinskikh, Sergey V.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Chain dynamics of surfactants in mesoporous silica2013Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 42, s. 18620-18626Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mesostructured porous materials possess unique surface, structural, and bulk properties that lead to important practical applications. By retaining structure-directing species in the product material, mesostructured organic-inorganic composites are obtained which are of broad interest for fundamental studies of confinement effects and surface interaction on structural and dynamic properties of organic molecules. In the present study, solid state dipolar C-13-H-1 NMR spectroscopy is applied to quantitatively characterize the conformational dynamics of organic surfactants in the mesostructured composite CTAB-MCM41. Such an approach does not require assumptions and adjustable parameters and reflects the changes in conformational dynamics without relying on specific motional models. The conformational dynamics of the surfactant confined in solid hexagonal arrays is compared to that in hexagonal aggregates formed in a concentrated aqueous solution. The study showed that in cylindrical pores of hexagonal mesoporous silica the order parameter gradually decreases towards the end of the chain. The degree of order and the order parameter profile is similar to that observed in hexagonal liquid crystalline phases. However, the mobility of segments close to the head group is more restricted compared to that in the mesophase, as the result of interaction with the solid silica interface.

  • 106.
    Khossossi, Nabil
    et al.
    Moulay Ismail Univ, Fac Sci, Dept Phys, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco.;Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, S-75120 Uppsala, Sweden..
    Banerjee, Amitava
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Benhouria, Younes
    Moulay Ismail Univ, Fac Sci, Dept Phys, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco..
    Essaoudi, Ismail
    Moulay Ismail Univ, Fac Sci, Dept Phys, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco.;Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, S-75120 Uppsala, Sweden..
    Ainane, Abdelmajid
    Moulay Ismail Univ, Fac Sci, Dept Phys, LP2MS,Unite Associee CNRST URAC 08, BP 11201, Meknes, Morocco.;Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, S-75120 Uppsala, Sweden.;Max Planck Inst Phys Complexer Syst, NothnitzerStr 38, D-01187 Dresden, Germany..
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, S-75120 Uppsala, Sweden..
    Ab initio study of a 2D h-BAs monolayer: a promising anode material for alkali-metal ion batteries2019Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, nr 33, s. 18328-18337Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The selection of a suitable two dimensional anode material is one of the key steps in the development of alkali metal ion batteries to achieve superior performance with an ultrahigh rate of charging/discharging capability. Here, we have used state of the art density functional theory (DFT) to explore the feasibility of two dimensional (2D) honeycomb boron arsenide (h-BAs) as a potential anode for alkali-metal (Li/Na/K)-ion batteries. The structural and dynamic stability has been confirmed from the formation energy and the non-negative phonon frequency. The h-BAs monolayer exhibits negative adsorption-energy values of -0.422, -0.321 and -0.814 eV, for the Li, Na, and K-ions, respectively. Subsequently, during the charging process the adsorption-energy increases considerably without an energy-barrier when any of the A-atoms achieve a crucial distance (similar to 8 angstrom). In addition, it has been observed that insertion of the mono alkali metal atom into the h-BAs surface results in the semi-conducting nature of the monolayer being transformed into a metallic-state. The low energy barriers for Li (0.522 eV), Na (0.248), and K (0.204 eV) active ion migration imply high diffusion over the h-BAs surface, hence suggesting it has a high charge/discharge capability. Moreover, we have obtained low average operating voltages of 0.49 V (Li), 0.35 V (Na) and 0.26 V (K) and high theoretical capacities of 522.08 mA h g(-1) (for Li and Na) and 209.46 mA h g(-1) (for K) in this study. The aforementioned findings indicate that a h-BAs monolayer could be a promising anode material in the search for low cost and high performance alkali metal ion batteries.

  • 107.
    Kuang, Guanglin
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Liang, Lijun
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Zhejiang University, China.
    Brown, Christian
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap.
    Wang, Qi
    Bulone, Vincent
    KTH, Skolan för bioteknologi (BIO), Glykovetenskap. Univ Adelaide, Australia.
    Tu, Yaoquan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Insight into the adsorption profiles of the Saprolegnia monoica chitin synthase MIT domain on POPA and POPC membranes by molecular dynamics simulation studies2016Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, nr 7, s. 5281-5290Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The critical role of chitin synthases in oomycete hyphal tip growth has been established. A microtubule interacting and trafficking (MIT) domain was discovered in the chitin synthases of the oomycete model organism, Saprolegnia monoica. MIT domains have been identified in diverse proteins and may play a role in intracellular trafficking. The structure of the Saprolegnia monoica chitin synthase 1 (SmChs1) MIT domain has been recently determined by our group. However, although our in vitro assay identified increased strength in interactions between the MIT domain and phosphatidic acid (PA) relative to other phospholipids including phosphatidylcholine (PC), the mechanism used by the MIT domain remains unknown. In this work, the adsorption behavior of the SmChs1 MIT domain on POPA and POPC membranes was systematically investigated by molecular dynamics simulations. Our results indicate that the MIT domain can adsorb onto the tested membranes in varying orientations. Interestingly, due to the specific interactions between MIT residues and lipid molecules, the binding affinity to the POPA membrane is much higher than that to the POPC membrane. A binding hotspot, which is critical for the adsorption of the MIT domain onto the POPA membrane, was also identified. The lower binding affinity to the POPC membrane can be attributed to the self-saturated membrane surface, which is unfavorable for hydrogen-bond and electrostatic interactions. The present study provides insight into the adsorption profile of SmChs1 and additionally has the potential to improve our understanding of other proteins containing MIT domains.

  • 108. Kulish, Vadym V.
    et al.
    Malyi, Oleksandr I.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. University of Oslo, Norway.
    Wu, Ping
    Adsorption of metal adatoms on single-layer phosphorene2015Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 2, s. 992-1000Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single- or few-layer phosphorene is a novel two-dimensional direct-bandgap nanomaterial. Based on first-principles calculations, we present a systematic study on the binding energy, geometry, magnetic moment and electronic structure of 20 different adatoms adsorbed on phosphorene. The adatoms cover a wide range of valences, including s and p valence metals, 3d transition metals, noble metals, semiconductors, hydrogen and oxygen. We find that adsorbed adatoms produce a rich diversity of structural, electronic and magnetic properties. Our work demonstrates that phosphorene forms strong bonds with all studied adatoms while still preserving its structural integrity. The adsorption energies of adatoms on phosphorene are more than twice higher than on graphene, while the largest distortions of phosphorene are only similar to 0.1-0.2 angstrom. The charge carrier type in phosphorene can be widely tuned by adatom adsorption. The unique combination of high reactivity with good structural stability is very promising for potential applications of phosphorene.

  • 109. Kulish, Vadym V.
    et al.
    Malyi, Oleksandr I.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. University of Oslo, Norway.
    Wu, Ping
    Phosphorene as an anode material for Na-ion batteries: a first-principles study2015Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 21, s. 13921-13928Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We systematically investigate a novel two-dimensional nanomaterial, phosphorene, as an anode for Na-ion batteries. Using first-principles calculations, we determine the Na adsorption energy, specific capacity and Na diffusion barriers on monolayer phosphorene. We examine the main trends in the electronic structure and mechanical properties as a function of Na concentration. We find a favorable Na-phosphorene interaction with a high theoretical Na storage capacity. We find that Na-phosphorene undergoes semiconductor-metal transition at high Na concentration. Our results show that Na diffusion on phosphorene is fast and anisotropic with an energy barrier of only 0.04 eV. Owing to its high capacity, good stability, excellent electrical conductivity and high Na mobility, monolayer phosphorene is a very promising anode material for Na-ion batteries. The calculated performance in terms of specific capacity and diffusion barriers is compared to other layered 2D electrode materials, such as graphene, MoS2, and polysilane.

  • 110. Leandri, V.
    et al.
    Ellis, H.
    Gabrielsson, Erik
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi. State Key Laboratory of Fine Chemicals, DUT-KTH Joint Research Center on Molecular Devices, Dalian University of Technology (DUT), China .
    Boschloo, G.
    Hagfeldt, A.
    An organic hydrophilic dye for water-based dye-sensitized solar cells2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 37, s. 19964-19971Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study we report the first organic hydrophilic dye employed for 100% water-based electrolyte DSSCs. We show that the replacement of alkyl by glycolic chains in the dye structure is able to provide excellent wettability, resulting in an efficient system with remarkably reduced desorption problems that allowed us to perform tests over a wide pH range. By changing the electrolyte composition, employing chenodeoxycholic acid as a co-adsorbent and using PEDOT counter-electrodes, 3% power conversion efficiency under 1-sun illumination was obtained. We show that chenodeoxycholic acid does not significantly increase the wettability, and we provide new insights into the higher performance resulting from its co-adsorption.

  • 111. Li, Bin
    et al.
    Ma, Ke
    Wang, Yong-Lei
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.). KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Turesson, Martin
    Woodward, Clifford E.
    Forsman, Jan
    Fused coarse-grained model of aromatic ionic liquids and their behaviour at electrodes2016Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, nr 11, s. 8165-8173Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A fused coarse-grained model of aromatic ionic liquids 1-alkyl-3-methylimidazoliums tetrafluoroborate ([CnMIM+][BF4-]) has been constructed. Structural and dynamical properties calculated from our model are compared with experimental data as well as with corresponding results from simulations of other suggested models. Specifically, we adopt a fused-sphere coarse-grained model for cations and anions. This model is utilized to study structure and differential capacitance in models of flat and porous carbon electrodes. We find that the capacitance varies with pore size, in a manner that is related to the packing of ions inside the pore. For very narrow pores, diffusion is slow and the establishment of thermodynamic equilibrium may exceed the practical limits for our molecular dynamics simulations.

  • 112.
    Li, Cui
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Inst Chem Phys Proc, Italy.
    Salen, Peter
    Yatsyna, Vasyl
    Schio, Luca
    Feifel, Raimund
    Squibb, Richard
    Kaminska, Magdalena
    Larsson, Mats
    Richter, Robert
    Alagia, Michele
    Stranges, Stefano
    Monti, Susanna
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Inst Chem Organometall Cpds, Italy.
    Carravetta, Vincenzo
    Zhaunerchyk, Vitali
    Experimental and theoretical XPS and NEXAFS studies of N-methylacetamide and N-methyltrifluoroacetamide2016Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, nr 3, s. 2210-2218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experimental Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectra of N-methyltrifluoroacetamide (FNMA), which is a peptide model system, measured at the C, N, O and F K-edges are reported. The features in the spectra have been assigned by Static-Exchange (STEX) calculations. Using the same method, we have also assigned previously measured NEXAFS spectra of another peptide model system, N-methylacetamide (NMA). To facilitate the NEXAFS feature assignments, X-ray Photoelectron Spectroscopy (XPS) measurements for NMA and FNMA have been carried out with the aim of obtaining the 1s electron ionization potentials, which are compared with the values predicted by our Hartree-Fock (Delta HF) and Multi Configuration Self Consistent Field (Delta MCSCF) calculations. We also demonstrate an approach to compensate for screening effects that are neglected in the STEX method. Ion yield measurements of FNMA associated with the excitation of several C, N, O, and F K-shell pre-edge resonances have revealed site-specific fragmentation in some cases which we interpret with the aid of our theoretical calculations.

  • 113. Li, Hongbao
    et al.
    Jiang, Jun
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Univ Sci & Technol China, Peoples R China.
    Identification of the protonation site of gaseous triglycine: the cis-peptide bond conformation as the global minimum2017Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 23, s. 15030-15038Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Extensive ab initio investigations have been performed to characterize stable conformers of protonated triglycine (GGGH) in the gas phase. Calculations using the composite CBS-QB3 method confirmed that the most favorable site of protonation on triglycine at 298 K is still the traditional amino nitrogen, rather than the more-recently reported amide oxygen. Furthermore, a non-proline cis-peptide bond conformer is identified for the first time as the global minimum of GGGH. Further transition state calculations considering the temperature effects explained why the previous experimental infrared multiple photon dissociation (IRMPD) spectrum contains a combination of two local minima, rather than a global one. First-principles simulations have been performed for near-edge X-ray absorption fine-structure (NEXAFS) spectra and X-ray photoelectron spectra (XPS) at the C, N and O K-edges to identify the notable spectral differences that enable the unambiguous identification of different protonated forms. The calculated proton affinity (PA) and gas basicity (GB) of triglycine are in excellent agreement with the experimental values. Our study thus provides valuable insights into the protonation of short peptides and illustrates the competition between cis and trans peptide bonds.

  • 114. Li, Hua
    et al.
    Rutland, Mark W.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Atkin, Rob
    Ionic liquid lubrication: influence of ion structure, surface potential and sliding velocity2013Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 35, s. 14616-14623Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Colloid probe atomic force microscopy (AFM) has been employed to investigate the nanotribology of the ionic liquid (IL)-Au(111) interface. Data is presented for four ILs, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([EMIM] FAP), 1-butyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate ([BMIM] FAP), 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([HMIM] FAP) and 1-butyl-3-methylimidazolium iodide ([BMIM] I), at different Au(111) surface potentials. Lateral forces vary as a function of applied surface potential and ion structure because the composition of the confined ion layer changes from cation-enriched (at negative potentials) to mixed (at 0 V), and to anion-enriched (at positive potentials). ILs with FAP(-) anions all exhibit similar nanotribology: low friction at negative potentials and higher friction at positive potentials. [BMIM] I displays the opposite behaviour, as an I- anion-enriched layer is more lubricating than either the [BMIM](+) or FAP(-) layers. The effect of cation charged group (charge-delocalised versus charged-localised) was investigated by comparing [BMIM] FAP with 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([Py-1,Py-4] FAP). [BMIM] FAP is less lubricating at negative potentials, but more lubricating at positive potentials. This indicated that even at positive potentials the cation concentration in the boundary layer is sufficiently high to influence lubricity. The influence of sliding velocity on lateral force was investigated for the [EMIM] FAP-Au(111) system. At neutral potentials the behaviour is consistent with a discontinuous sliding process. When a positive or negative potential bias is applied, this effect is less pronounced as the colloid probe slides along a better defined ion plane.

  • 115. Li, Hua
    et al.
    Somers, Anthony E.
    Howlett, Patrick C.
    Rutland, Mark W.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. SP Technical Research Institute of Sweden, Sweden.
    Forsyth, Maria
    Atkin, Rob
    Addition of low concentrations of an ionic liquid to a base oil reduces friction over multiple length scales: a combined nano- and macrotribology investigation2016Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, nr 9, s. 6541-6547Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The efficacy of ionic liquids (ILs) as lubricant additives to a model base oil has been probed at the nanoscale and macroscale as a function of IL concentration using the same materials. Silica surfaces lubricated with mixtures of the IL trihexyl(tetradecyl) phosphonium bis(2,4,4-trimethylpentyl)phosphinate and hexadecane are probed using atomic force microscopy (AFM) (nanoscale) and ball-on-disc tribometer (macroscale). At both length scales the pure IL is a much more effective lubricant than hexadecane. At the nanoscale, 2.0 mol% IL (and above) in hexadecane lubricates the silica as well as the pure IL due to the formation of a robust IL boundary layer that separates the sliding surfaces. At the macroscale the lubrication is highly load dependent; at low loads all the mixtures lubricate as effectively as the pure IL, whereas at higher loads rather high concentrations are required to provide IL like lubrication. Wear is also pronounced at high loads, for all cases except the pure IL, and a tribofilm is formed. Together, the nano- and macroscales results reveal that the IL is an effective lubricant additive - it reduces friction - in both the boundary regime at the nanoscale and mixed regime at the macroscale.

  • 116.
    Li, Xin
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Zhang, Qiong
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Tu, Yaoquan
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Tian, He
    Modulation of iridium(III) phosphorescence via photochromic ligands: a density functional theory study2010Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, nr 41, s. 13730-13736Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The photochromic iridium(III) complex (Py-BTE)(2)Ir(acac) synthesized by Tan et al. [W. Tan et al., Org. Lett. 2009, 11, 161-164] has shown distinct photo-reactivity and photo-controllable phosphorescence. We here present a density functional theory study on the (Py-BTE)(2)Ir(acac) complex to explore the mechanism at the molecular level and to help further design of photochromic iridium(III) complexes with the desirable properties. The hybrid functional PBE0, with 25% Hartree-Fock exchange, is found to give an optimal structure compared with X-ray crystallographic data. The absorption bands are well reproduced by using time-dependent density functional theory calculations, lending the possibility to assign the metal-to-ligand and intra-ligand charge transfer transitions. The radiative and nonradiative deactivation rate constants, k(r) and k(nr), are rationalized for both the open-ring and closed-ring forms of the complex. The very large k(nr) and small k(r) make the closed-ring form of the complex non-emissive. The triplet reactivity of the Py-BTE ligand is also studied by performing density functional theory calculations on the potential energy surfaces of the ground state and the lowest triplet state.

  • 117.
    Li, Xin
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Zhu, Liangliang
    Duan, Sai
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Zhao, Yanli
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Aggregation-induced chiral symmetry breaking of a naphthalimide-cyanostilbene dyad2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 43, s. 23854-23860Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spontaneously emerged supramolecular chirality and chiral symmetry breaking from achiral/racemic constituents remain poorly understood. We here report that supramolecular chirality may emerge from the structural flexibility of achiral aryl nitrogen centres which provide instantaneous chirality. Employing a naphthalimide-cyanostilbene dyad as a model, we explored the underlying mechanism of aggregation-induced chiral symmetry breaking and found that the conformations of the N-naphthylpiperazine and the N, N-dimethylaniline units facilitate the formation of ordered supramolecular structures and offer opposite handedness. Furthermore, chiral symmetry breaking of the monomers was amplified by the formation of dimers. The microscopic and the macroscopic observations from the theoretical simulations and experimental measurements are thus rationalized by connecting the population of the dihedral angles of the aryl nitrogen centres, the morphology of the self-assemblies, and the observed circular dichroism spectra.

  • 118.
    Liljeblad, Jonathan F. D.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Furo, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Tyrode, Eric C.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    The premolten layer of ice next to a hydrophilic solid surface: correlating adhesion with molecular properties2017Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 1, s. 305-317Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In order to establish the potential correlation between the macroscopic ice adhesion and the molecular properties of the premolten layer (PML), the adhesion strength between ice and hydrophilic silica has been measured as a function of temperature. In addition, temperature-dependent molecular properties have been determined using techniques that are sensitive to different aspects of the PML, specifically total internal reflection (TIR) Raman, vibrational sum frequency (VSFS) and NMR spectroscopies. The ice shear adhesion strength was observed to increase linearly with decreasing temperature until -25 degrees C, where a plateau marked the adhesive strength having reached the cohesive strength of ice. Interestingly, at temperatures higher than -20 degrees C the ice samples slid on smooth (R-a < 0.4 nm) silica surfaces. This sliding behavior was not observed on rougher silica surfaces (R-a similar to 6 nm). By varying the penetration depth of the evanescent field, TIR Raman was used to establish an upper limit to the thickness of the PML in contact with silica (<3 nm even at -0.3 K below the bulk melting temperature). Additional quantitative determination of the temperature-dependent thickness of the PML was obtained from H-2 NMR measurements in mesoporous silica particles. Finally, the inherently surface specific technique, VSFS, which probed changes in the hydrogen bond environment, indicated at approximately -25 degrees C the onset of PML, followed by a marked structural change occurring just a fraction of a degree below the melting temperature. Jointly, the experimental approaches link, strongly and consistently, ice adhesion to the PML properties. Specifically, it is inferred that the premolten layer facilitates sliding and contributes to the observed friction behavior, provided its thickness is comparable to the surface roughness of the underlying silica substrate.

  • 119.
    Liljeblad, Jonathan F. D.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Tyrode, Eric
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Thormann, Esben
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Department of Chemistry, Technical University of Denmark, Kemitorvet 207, DK-2800 Kgs. Lyngby, Denmark.
    Dublanchet, Ann-Claude
    L’Oréal Research and Innovation, Aulnay-sous-Bois, France.
    Luengo, Gustavo
    L’Oréal Research and Innovation, Aulnay-sous-Bois, France.
    Johnson, C. Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Rutland, Mark W
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Self-assembly of long chain fatty acids: effect of a methyl branch2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 33, s. 17869-17882Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The morphology and molecular conformation of Langmuir Blodgett deposited and floating monolayers of a selection of straight chain (eicosanoic acid, EA), iso (19-methyl eicosanoic acid, 19-MEA), and anteiso (18-methyl eicosanoic acid, 18-MEA) fatty acids have been investigated by Vibrational Sum Frequency Spectroscopy (VSFS), AFM imaging, and the Langmuir trough. While the straight chain fatty acid forms smooth, featureless monolayers, all the branched chain fatty acids display 10-50 nm sized domains (larger for 19-MEA than the 18-MEA) with a homogeneous size distribution. A model is suggested to explain the domain formation and size in terms of the branched fatty acid packing properties and the formation of hemispherical caps at the liquid air interface. No difference between the chiral (S) form and the racemic mixture of the 18-MEA is observed with any of the utilized techniques. The aliphatic chains of the straight chain fatty acids appear to be oriented perpendicular to the sample surface, based on an orientational analysis of VSFS data and the odd/even effect. In addition, the selection of the subphase (neat water or CdCl2 containing water buffered to pH 6.0) used for the LB-deposition has a profound influence on the monolayer morphology, packing density, compressibility, and conformational order. Finally, the orientation of the 19-MEA dimethyl moiety is estimated, and a strategy for performing an orientational analysis to determine the complete molecular orientation of the aliphatic chains of 19-MEA and 18-MEA is outlined and discussed.

  • 120.
    Linares, Mathieu
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Sun, Haofan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi. East China Univ Sci & Technol, Shanghai Key Lab Funct Mat Chem, Dept Chem & Mol Engn, Shanghai 200237, Peoples R China.
    Biler, Michal
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Andreasson, Joakim
    Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden..
    Norman, P.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Elucidating DNA binding of dithienylethenes from molecular dynamics and dichroism spectra2019Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, nr 7, s. 3637-3643Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    DNA binding modes of the stereoisomeric rotamers of two dithenylethene derivatives (DTE1 and DTE2) representing candidate molecular photoswitches of great promise for photopharmacology and nanotechnology have been identified and characterized in terms of their binding energies and electronic circular dichroism (CD) responses. In the open form, two binding modes are identified namely minor-groove binding of the lowest-energy conformer with an anti-parallel arrangement of methyl groups and major-groove double-intercalation of the P-enantiomers of an intermediate-state rotamer. Only the latter binding mode is found to be enantiomerically selective and expected to have an overall negative linear dichroism (LD) as observed in the experiment for DTE1 (Angew. Chem., Int. Ed., 2013, 52, 4393). In the closed form, the most favorable binding mode is found to be minor groove binding. Also this binding mode is found to be enantiomerically selective and for DTE1, it is the M-enantiomer that binds the strongest, showing a positive theoretical signature CD band in the long wavelength region with origin in pyridinium ligands. The theoretical CD spectrum is found to be in good agreement with the experimental one, which provides an indirect evidence for a correct identification of the binding mode in the closed form.

  • 121. Lindblad, Rebecka
    et al.
    Cappel, Ute B
    O'Mahony, Flannan T F
    Siegbahn, Hans
    Johansson, Erik M J
    Haque, Saif A
    Rensmo, Håkan
    Energy level alignment in TiO2/metal sulfide/polymer interfaces for solar cell applications.2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 32, s. 17099-107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Semiconductor sensitized solar cell interfaces have been studied with photoelectron spectroscopy to understand the interfacial electronic structures. In particular, the experimental energy level alignment has been determined for complete TiO2/metal sulfide/polymer interfaces. For the metal sulfides CdS, Sb2S3 and Bi2S3 deposited from single source metal xanthate precursors, it was shown that both driving forces for electron injection into TiO2 and hole transfer to the polymer decrease for narrower bandgaps. The energy level alignment results were used in the discussion of the function of solar cells with the same metal sulfides as light absorbers. For example Sb2S3 showed the most favourable energy level alignment with 0.3 eV driving force for electron injection and 0.4 eV driving force for hole transfer and also the most efficient solar cells due to high photocurrent generation. The energy level alignment of the TiO2/Bi2S3 interface on the other hand showed no driving force for electron injection to TiO2, and the performance of the corresponding solar cell was very low.

  • 122.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    On the method-dependence of transition state asynchronicity in Diels-Alder reactions2013Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 14, s. 5108-5114Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work discusses the dependence of transition state geometries on the choice of quantum chemical optimization method for the extensively studied Diels-Alder reaction. Rather significant differences are observed between post-Hartree-Fock methods and (hybrid) density functional theory, where the latter predicts larger asynchronicities. The results show that the low MP2 asynchronicity observed is likely artificial. Still, there are significant discrepancies between hybrid and pure density functionals. The role of the exchange functional seems to be most prominent in less activated reacting systems, while the importance of the correlation functional seems to increase as they become more activated by, e. g., an electron-donating group on the diene. To correct the dubious MP2 geometries, we employed the SCS-MP2 protocol for transition state optimization, which leads to significantly better results with respect to CCSD/6-31+G(d) level calculations. We conclude that in order for hybrid functionals to give descriptions consistent with the sample post-Hartree-Fock methods, a balanced combination of both Hartree-Fock exchange (with a couple of exceptions) and a well-behaved correlation functional is required. Given that the benchmark CCSD/6-31+ G(d) geometries are sufficient representations, the best geometries were obtained using omega B97X(D), B2PLYP(D) and M06-2X.

  • 123.
    Lindh, Erik L.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Terenzi, Camilla
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Salmén, Lennart
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Furo, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Water in cellulose: evidence and identification of immobile and mobile adsorbed phases by H-2 MAS NMR2017Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 6, s. 4360-4369Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The organization of water molecules adsorbed onto cellulose and the supramolecular hydrated structure of microfibril aggregates represents, still today, one of the open and complex questions in the physical chemistry of natural polymers. Here, we investigate by H-2 MAS NMR the mobility of water molecules in carefully H-2-exchanged, and thereafter re-dried, microcrystalline cellulose. By subtracting the spectral contribution of deuteroxyls from the spectrum of hydrated cellulose, we demonstrate the existence of two distinct (H2O)-H-2 spectral populations associated with mobile and immobile water environments, between which the water molecules do not exchange at the NMR observation time scale. We conclude that those two water phases are located at differently-accessible adsorption sites, here assigned to the cellulose surfaces between and within the microfibril aggregates, respectively. The superior performance of H-2 MAS NMR encourages further applications of the same method to other complex systems that expose heterogeneous hygroscopic surfaces, like wood cell walls.

  • 124.
    List, Nanna Holmgaard
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Olsen, Jogvan Magnus Haugaard
    Kongsted, Jacob
    Excited states in large molecular systems through polarizable embedding2016Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, nr 30, s. 20234-20250Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this perspective, we provide an overview of recent work within the polarizable embedding scheme to describe properties of molecules in realistic environments of increasing complexity. After an outline of the theoretical basis for the polarizable embedding model, we discuss the importance of using an accurate embedding potential, and how this may be used to significantly reduce the size of the part of the system treated using quantum mechanics without compromising the accuracy of the final results. Furthermore, we discuss the calculation of local electronic excited states based on response theory. We finally discuss aspects related to two recent extensions of the model (i) effective external field and (ii) polarizable density embedding emphasizing their importance for efficient yet accurate description of excited-state properties in complex environments.

  • 125. Liu, J.
    et al.
    Yang, X.
    Cong, J.
    Kloo, Lars
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD. Dalian Univ Technol, China.
    Solvent-free ionic liquid electrolytes without elemental iodine for dye-sensitized solar cells2012Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, nr 33, s. 11592-11595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new type of electrolyte with a sulfide/polysulfide redox couple and I - was prepared as a solvent-free ionic liquid for application in dye-sensitized solar cells, reaching efficiencies of 5.2-6.4% under AM 1.5G, 100 mW cm -2 light illumination, and 6.6% efficiency was obtained under 0.1 sun irradiation.

  • 126. Liu, Lingling
    et al.
    Li, Xiao-Fei
    Yan, Qing
    Li, Qin-Kun
    Zhang, Xiang-Hua
    Deng, Mingsen
    Qiu, Qi
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Uniform and perfectly linear current-voltage characteristics of nitrogen-doped armchair graphene nanoribbons for nanowires2017Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 1, s. 44-48Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metallic nanowires with desired properties for molecular integrated circuits (MICs) are especially significant in molectronics, but preparing such wires at a molecular level still remains challenging. Here, we propose, from first principles calculations, experimentally realizable edge-nitrogen-doped graphene nanoribbons (N-GNRs) as promising candidates for nanowires. Our results show that edge N-doping has distinct effects on the electronic structures and transport properties of the armchair GNRs and zigzag GNRs (AGNRs, ZGNRs), due to the formation of pyridazine and pyrazole rings at the edges. The pyridazine rings raise the Fermi level and introduce delocalized energy bands near the Fermi level, resulting in a highly enhanced conductance in N-AGNRs at the stable nonmagnetic ground state. Especially for the family of AGNRs with widths of n = 3p + 2, their semiconducting characteristics are transformed to metallic characteristics via N-doping, and they exhibit perfectly linear current-voltage (I-V) behaviors. Such uniform and excellent features indicate bright application prospects of the N-AGNRs as nanowires and electrodes in molectronics.

  • 127.
    Liu, Peng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Nisar, Jawad
    Pathak, Biswarup
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Cationic-anionic mediated charge compensation on La2Ti2O7 for visible light photocatalysis2013Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 40, s. 17150-17157Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The cationic-anionic mediated charge compensation effect was studied in the layered perovskite La2Ti2O7 for the visible light photocatalysis. Our screened hybrid density functional study shows that the electronic structure of La2Ti2O7 can be tuned by the cationic (V, Nb, Ta)/anionic (N) mono-and co-doping. Such mono-doping creates impurity states in the band gap which helps the electron-hole recombination. But if the charge compensation is made by the cationic-anionic mediated co-doping then such impurity states can be removed and can be a promising strategy for visible light photocatalysis. The absolute band edge position of the doped La2Ti2O7 has been aligned with respect to the water oxidation/reduction potential. The calculated defect formation energy shows the stability of the co-doping system is improved due to the coulomb interactions and charge compensations effect.

  • 128.
    Lousada, Claudio M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi. RAS, Ural Div, Inst Met Phys, Ekaterinburg 620219, Russia..
    The first stages of oxide growth at the low index Al surfaces (100), (110), (111): clusters and stripes vs. homogeneous growth2018Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 46, s. 29549-29557Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed a density functional theory (DFT) investigation of the mechanisms of oxide growth at Al(100), Al(110) and Al(111) up to 1 monolayer (ML) coverage of O-atoms with 0.125 ML increments. We found that the surface binding site preferences of O-atoms are largely affected by the presence of neighboring O-atoms. Based on this we constructed two oxide growth models: the formation of clusters that evolve to stripes with increasing coverage and the formation of a more homogeneous distribution of O-atoms. While the former model is characterized by a lower symmetry of distribution of O-atoms at the surfaces, the latter corresponds to higher symmetries. We found that the prevalence of each oxide growth mode depends on the coverage of O-atoms and that this dependency is different for each surface. For Al(100) and Al(110), up to coverages of 1 ML the oxide grows preferably via the formation of clusters that evolve to stripes with increasing coverage, while for Al(111) the stripes and clusters are the preferred growth mode for coverages up to 0.375 ML, beyond which the homogeneous growth mode is energetically favored. The calculated Al-O pair distribution functions show that the formation of clusters and stripes leads to shorter Al-O bond lengths when compared to the homogeneous growth. The oxides formed at Al(100) and Al(110) have Al-O bond lengths and geometries typical of the shorter bonds of -alumina while at Al(111) the bond lengths are typical of -alumina and -alumina. These results suggest that for low coverages, the oxides formed at Al(100) and Al(110) are resemblant of defective -alumina while the oxide formed at Al(111) is similar to less disordered -alumina and -alumina. For Al(111), the small energy difference between the growth of clusters and stripes and homogeneous growth does not exclude the coexistence of both growth modes; this could lead to the formation of a defective or amorphous oxide.

  • 129.
    Lousada, Claudio M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Oxygen adsorption onto pure and doped Al surfaces - the role of surface dopants2015Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 3, s. 1667-1679Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using density functional theory (DFT) with the PBE0 density functional we investigated the role of surface dopants in the molecular and dissociative adsorption of O-2 onto Al clusters of types Al-50, Al50Alad, Al50X and Al49X, where X represents a dopant atom of the following elements Si, Mg, Cu, Sc, Zr, and Ti. Each dopant atom was placed on the Al(111) surface as an adatom or as a substitutional atom, in the last case replacing a surface Al atom. We found that for the same dopant geometry, the closer is the ionization energy of the dopant element to that of elemental Al, the more exothermic is the dissociative adsorption of O-2 and the stronger are the bonds between the resulting O atoms and the surface. Additionally we show that the Mulliken concept of electronegativity can be applied in the prediction of the dissociative adsorption energy of O-2 on the doped surfaces. The Mulliken modified second-stage electronegativity of the dopant atom is proportional to the exothermicity of the dissociative adsorption of O-2. For the same dopant element in an adatom position the dissociation of O-2 is more exothermic when compared to the case where the dopant occupies a substitutional position. These observations are discussed in view of the overlap population densities of states (OPDOS) computed as the overlap between the electronic states of the adsorbate O atoms and the clusters. It is shown that a more covalent character in the bonding between the Al surface and the dopant atom causes a more exothermic dissociation of O-2 and stronger bonding with the O atoms when compared to a more ionic character in the bonding between the dopant and the Al surface. The extent of the adsorption site reconstruction is dopant atom dependent and is an important parameter for determining the mode of adsorption, adsorption energy and electronic structure of the product of O-2 adsorption. The PBE0 functional could predict the existence of the O-2 molecular adsorption product for many of the cases investigated here.

  • 130.
    Lousada, Claudio Miguel
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    LaVerne, Jay A.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Enhanced hydrogen formation during the catalytic decomposition of H2O2 on metal oxide surfaces in the presence of HO radical scavengers2013Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 30, s. 12674-12679Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Presently and for the foreseeable future, hydrogen peroxide and transition metal oxides are important constituents of energy production processes. In this work, the effect of the presence of HO radical scavengers on the product yield from the decomposition of H2O2 on metal oxide surfaces in aqueous solution was examined experimentally. Scavenging the intermediate product HO center dot by means of Tris or TAPS buffer leads to enhanced formation of H-2. In parallel, a decrease in the production of the main gaseous product O-2 is observed. Under these conditions, H-2 formation is a spontaneous process even at room temperature. The yields of both the H-2 and O-2 depend on the concentration of Tris or TAPS in the reaction media. We observed that TAPS has a higher affinity for the surface of ZrO2 than does Tris. The difference in adsorption of both scavengers is reflected by the difference in their influence on the product yields. The observed sensitivity of the system H2O2-ZrO2 towards the two different scavengers indicates that O-2 and H-2 are formed at different types of surface sites.

  • 131.
    Lousada, Cláudio M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Johansson, Adam Johannes
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Molecular and dissociative adsorption of water and hydrogen sulfide at perfect and defective Cu(110) surfaces2017Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, s. 8111-8120Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed a density functional theory (DFT) investigation of the molecular and dissociative adsorption of H2O and H2S at perfect and defective Cu(110) surfaces described using supercells with c(6 × 6) periodicity. The defective surface consists of a terrace surrounded by pits. We found considerable differences in adsorption modes and energies for H2O and H2S. At the defective Cu(110) surface, monomers of H2O and H2S preferentially adsorb at the terrace site and molecular adsorption of H2O is significantly more favorable than that of H2S. For dissociative adsorption however, the sulfur species are considerably more stable than the oxygen species. For monolayer (ML) coverages, there are small differences in the molecular adsorption energies for H2O and H2S. However, for the formation of 1 ML of HO and 1 ML of HS from 1 ML of H2O and 1 ML of H2S, respectively, with the release of H2(g), the differences are very large. The formation of 1 ML HO at the perfect Cu(110) surface is endoergic, while at the defective Cu(110) surface it is exoergic by −0.6 eV. For high coverages, H2S forms stacked half-monolayers that interact with each other via a complex hydrogen bond network with a strength per H2S molecule of −0.140 eV per H2S and −0.120 eV per H2S for H2S located in the underlayer and overlayer, respectively. The large distances between hydrogen bonded H2S molecules explain the preference for the formation of the two stacked half-monolayers of H2S instead of a single monolayer as it happens with H2O. Additionally, the formation of 1 ML of HS does not occur because of the spontaneous splitting of some H–S bonds resulting in surface bound HS and S and H2S molecules. Extensive surface reconstruction and relaxation accompanies adsorption of the sulfur adsorbates. Such reconstructions with outwards pull of Cu atoms can be at the origin of the weak adhesion of sulfide films that explains the release of CuS particles from copper sulfide films at copper surfaces. Overall, the surface defects here investigated induce non-linear effects in the molecular and dissociative adsorption energies of different O and S adsorbates.

  • 132.
    Lousada Patricio, Cláudio Miguel
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Johansson, Adam Johannes
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Reactivity of metal oxide clusters with hydrogen peroxide and water: a DFT study evaluating the performance of different exchange-correlation functionals2013Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 15, s. 5539-5552Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have performed a density functional theory (DFT) investigation of the interactions of H2O2, H2O and HO radicals with clusters of ZrO2, TiO2 and Y2O3. Different modes of H2O adsorption onto the clusters were studied. In almost all the cases the dissociative adsorption is more exothermic than molecular adsorption. At the surfaces where H2O has undergone dissociative adsorption, the adsorption of H2O2 and the transition state for its decomposition are mediated by hydrogen bonding with the surface HO groups. Using the functionals B3LYP, B3LYP-D and M06 with clusters of 26 and 8 units of ZrO2, the M06 functional performed better than B3LYP in describing the reaction of decomposition of H2O2 and the adsorption of H2O. Additionally, we investigated clusters of the type (ZrO2)2, (TiO2)2 and (Y2O3) and the performance of the functionals B3LYP, B3LYP-D, B3LYP*, M06, M06-L, PBE0, PBE and PWPW91 in describing H2O2, H2O and HO˙ adsorption and the energy barrier for decomposition of H2O2. The trends obtained for HO˙ adsorption onto the clusters are discussed in terms of the ionization energy of the metal cation present in the oxide. In order to correctly account for the existence of an energy barrier for the decomposition of H2O2, the functional used must include Hartree-Fock exchange. Using minimal cluster models, the best performance in describing the energy barrier for H2O2 decomposition was obtained with the M06 and PBE0 functionals - the average absolute deviations from experiments are 6 kJ mol(-1) and 5 kJ mol(-1) respectively. With the M06 functional and a larger monoclinic (ZrO2)8 cluster model, the performance is in excellent agreement with experimental data. For the different oxides, PBE0 was found to be the most effective functional in terms of performance and computational time cost.

  • 133. Lu, H.
    et al.
    Zhang, H.
    Yuan, S.
    Wang, J.
    Zhan, Y.
    Zheng, Lirong
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Elektronik, Integrerade komponenter och kretsar. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. Fudan University, China.
    An optical dynamic study of MAPbBr3 single crystals passivated with MAPbCl3/I3-MAPbBr3 heterojunctions2017Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, nr 6, s. 4516-4521Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recently, perovskite based solar cells have attracted lots of research interest, some of which is in the passivation of perovskite surfaces, particularly the heterojunction based surface passivation. In this study, the optical dynamics of MAPbBr3 single crystals with and without heterojunction passivation were studied systematically by means of a time-resolved spectroscopic technique for the first time. The emission lifetime of MAPbBr3 single crystals under two-photon (1064 nm) excitation is a few orders of magnitude longer than that measured under one-photon (355 nm or 532 nm) excitation. Interestingly, with surface passivation, the lifetime measured at 355 nm excitations could be tuned significantly, whereas the lifetime change under 1064 nm excitations was considerably less. Our results give a direct evidence of surface quench by comparing the lifetimes before and after surface passivation. Furthermore, the results demonstrate that proper MAPbCl3-MAPbBr3 heterojunctions can dramatically reduce the recombination channels in the surface region, which can be potentially useful for perovskite based solar cells, light emitting diodes (LED), and sensitive detectors.

  • 134. Madsen, Diana
    et al.
    Christiansen, Ove
    König, Carolin
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Anharmonic vibrational spectra from double incremental potential energy and dipole surfaces2018Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 5, s. 3445-3456Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We extend the fragmentation-based double incremental expansion in FALCON coordinates (DIF) and its linear-scaling analogue [C. Konig and O. Christiansen, J. Chem. Phys., 2016, 145, 064105] to dipole surfaces. Thereby, we enable the calculation of intensities in vibrational absorption spectra from these cost-efficient property surfaces. We validate the obtained potential energy and dipole surfaces by vibrational spectra calculations employing damped response theory for correlated vibrational coupled cluster wave functions. Our largest calculation on a hexa-phenyl includes all 180 vibrational degrees of freedom of the system, which illustrates the potential of both the DIF schemes for property surface generation and the use of damped response theory from high-dimensional correlated vibrational wave functions. Generally, we obtain good agreement between the spectra calculated from the DIF property surfaces and the non-fragmented analogues. Moreover, when adopting suitable electronic structure methods, good agreement with respect to the experiment can be obtained, as shown for the example of 5-methylfurfural and RI-MP2. In conclusion, our results illustrate that the presented scheme with linearly scaling surfaces enables high quality spectra, as long as reasonably sized fragments can be defined. With this work, we push the realistic limits of vibrational spectra calculations from vibrational wave function methods and accurate electronic structure calculations to significantly larger systems than currently accessible.

  • 135.
    Madsen, Diana
    et al.
    Aarhus Univ, Dept Chem, Langelandsgade 140, DK-8000 Aarhus C, Denmark..
    Christiansen, Ove
    Aarhus Univ, Dept Chem, Langelandsgade 140, DK-8000 Aarhus C, Denmark..
    Norman, Patrick
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Koenig, Carolin
    Christian Albrechts Univ Kiel, Inst Phys Chem, Max Eyth Str 1, D-24118 Kiel, Germany..
    Vibrationally resolved emission spectra of luminescent conjugated oligothiophenes from anharmonic calculations2019Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, nr 31, s. 17410-17422Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on accurate and efficient calculations of vibrationally resolved emission spectra for oligothiophenes from anharmonic vibrational configuration interaction wave-function calculations in reduced vibrational spaces. These reduced spaces are chosen based on the independent mode displaced harmonic oscillator model. Good agreement with experiment is obtained for all-trans oligothiophenes with two to five rings also when employing only a few active modes. Vibrational modes incorporating inter-ring carbon-carbon stretches and a ring breathing mode are found to be the main players in the vibrational progression for the emission from the first excited electronic state for all investigated oligothiophene derivatives. The presented framework is here illustrated for oligothiophenes, but we have made no underlying system-dependent assumptions and believe it to become a valuable tool for the rational design of fluorescence biomarkers.

  • 136. Malyi, Oleksandr I.
    et al.
    Bostroem, Mathias
    Kulish, Vadym V.
    Thiyam, Priyadarshini
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Parsons, Drew F.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Univ Oslo, Ctr Mat Sci & Nanotechnol, Norway.
    Volume dependence of the dielectric properties of amorphous SiO22016Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, nr 10, s. 7483-7489Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using first principles calculations, the analysis of the dielectric properties of amorphous SiO2 (am-SiO2) was performed. We found that the am-SiO2 properties are volume dependent, and the dependence is mainly induced by the variation of nanoporosity at the atomic scale. In particular, both ionic and electronic contributions to the static dielectric constants are functions of volume with clear trends. Moreover, using the unique parameterization of the dielectric function provided in this work, we predict dielectric functions at imaginary frequencies of different SiO2 polymorphs having similar band gap energies.

  • 137. Malyi, Oleksandr I.
    et al.
    Thiyam, Priyadarshini
    Boström, Mathias
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Univ Oslo, Norway.
    A first principles study of CO2 adsorption on alpha-SiO2(001) surfaces2015Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 31, s. 20125-20133Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, using first principles calculations, an analysis of CO2 interaction with cleaved and reconstructed alpha-SiO2(001) surfaces was performed. We showed that CO2 could strongly interact with a cleaved surface forming CO3-like configurations. Here, the binding energy per CO2 molecule depends strongly on CO2 surface coverage and can reach -2.35 eV. Despite this, even with CO2 molecules, the cleaved surface has a substantially higher surface energy than that of the reoptimized "dense'' surface. This observation is also consistent with molecular dynamics simulations. Because of this, for thermodynamically stable system, the interaction of CO2 molecules with a alpha-SiO2(001) surface should be treated as the physisorption of CO2 molecules on the reoptimized "dense'' surface with the binding energy varying from -0.26 eV for single CO2 molecule adsorption to -0.32 eV per molecule for monolayer coverage.

  • 138. Migas, D. B.
    et al.
    Filonov, A. B.
    Borisenko, V. E.
    Skorodumova, Natalia V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. Department of Physics and Astronomy, Uppsala University, Sweden.
    Orientation effects in morphology and electronic properties of anatase TiO2 one-dimensional nanostructures. II. Nanotubes2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 20, s. 9490-9498Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the first part [D. B. Migas et al., Phys. Chem. Chem. Phys., 2014, DOI: 10.1039/C3CP54988G] by means of ab initio calculations we have analyzed and discussed anisotropy effects on electronic properties of 001 -, 100 - and 110 - oriented anatase TiO2 nanowires. In this part we present results indicating crucial changes in morphology of anatase TiO2 nanotubes originating from TiO2 nanowires by making a hole along the wire axis. The critical wall thickness has been found to exist for the nanotubes with 001 and 110 axes: at smaller thickness their shape can be rounded, squeezed, viewed as conglomerates of nanocrystals and even represented as cylindrical and `single-walled'- like structures formed without rolling up a thin titania layer into a nanotube. In general, band dispersion near the gap region of TiO2 nanotubes is close to the one of TiO2 nanowires with the same orientation. We have also revealed that optimization of the unit cell parameter along the wire axis and consideration of quantum confinement and surface state effects are important to provide an interpretation of band-gap variation with respect to wall thickness in TiO2 nanotubes.

  • 139. Migas, Dmitri B.
    et al.
    Filonov, Andrew B.
    Borisenko, Victor E.
    Skorodumova, Natalia V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Orientation effects in morphology and electronic properties of anatase TiO2 one-dimensional nanostructures. I. Nanowires2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 20, s. 9479-9489Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By means of ab initio calculations we have revealed the existence of sizable anisotropy in electronic properties of anatase TiO2 nanowires with respect to orientation: nanowires with 001 , 100 and 110 axes are found to be direct band-gap, indirect band-gap and degenerate semiconductor materials, respectively. The degenerate semiconducting properties of 110 oriented TiO2 nanowires are predicted to be the intrinsic features closely connected with stoichiometry. A band-gap variation with nanowire diameter is also shown to display rather complex behavior characterized by a competition between quantum confinement and surface state effects that is fully compatible with the available contradictory experimental data. Finally, we propose a model to explain the band-gap variation with size in TiO2 nanowires, nanocrystals and thin films.

  • 140. Milne, B. F.
    et al.
    Norman, P.
    Nogueira, F.
    Cardoso, C.
    Marine natural products from the deep Pacific as potential non-linear optical chromophores2013Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 35, s. 14814-14822Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theoretical analysis using quadratic response theory within the time-dependent density functional theory (TDDFT) formalism shows that the dermacozines, a group of phenazine-based compounds isolated from cultures of Dermacoccus abyssi found in the Mariana Trench, possess large first hyperpolarisability (β) values at common incident laser wavelengths that are highly sensitive to the degree and type of substitution of the core structure. The phenazine moiety is a versatile and tunable chromophore for non-linear optics and this work serves to highlight the potential that (marine) natural products, even those found in the darkest places on the planet, may have for aiding developments in optical materials design. This journal is © the Owner Societies 2013.

  • 141.
    Minaev, Boris
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Baryshnikov, Gleb
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Principles of phosphorescent organic light emitting devices2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 5, s. 1719-1758Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Organic light-emitting device (OLED) technology has found numerous applications in the development of solid state lighting, flat panel displays and flexible screens. These applications are already commercialized in mobile phones and TV sets. White OLEDs are of especial importance for lighting; they now use multilayer combinations of organic and elementoorganic dyes which emit various colors in the red, green and blue parts of the visible spectrum. At the same time the stability of phosphorescent blue emitters is still a major challenge for OLED applications. In this review we highlight the basic principles and the main mechanisms behind phosphorescent light emission of various classes of photofunctional OLED materials, like organic polymers and oligomers, electron and hole transport molecules, elementoorganic complexes with heavy metal central ions, and clarify connections between the main features of electronic structure and the photo-physical properties of the phosphorescent OLED materials.

  • 142.
    Mohammed, Abdelsalam
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Norman, Patrick
    Time-dependent density functional theory for resonant properties: resonance enhanced Raman scattering from the complex electric-dipole polarizability2009Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, nr 22, s. 4539-4548Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Based on resonant-convergent-and thereby complex-electric-dipole polarizabilities, formulae for differential cross sections in resonant Raman spectroscopy are presented. In absorptive regions of the spectrum, there are phase delays in the induced polarization that enter the expressions for the cross sections. The theory is exemplified by calculations employing the adiabatic time-dependent density functional theory approximation, with applications on the low-lying, dipole-allowed, electronic states of a sample of molecules, including hydrogen peroxide, pyridine, and trinitrotoluene. Results obtained with the Coulomb attenuated B3LYP exchange-correlation functional are found to be more accurate than those obtained with the conventional B3LYP functional-an observation that holds not only for trinitrotoluene with its transitions of charge-transfer character but also for the other cases. The qualitative features of the resonant Raman spectra for a given molecule vary strongly from one resonance wavelength to another, which is a fact that could further facilitate the use of this spectroscopy in applications of stand-off detection of gaseous samples in ultra-low concentrations.

  • 143. Murugan, N. Arul
    et al.
    Hugosson, Håkan Wilhelm
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Investigations into conformational transitions and solvation structure of a 7-piperidino-5,9-methanobenzo 8 annulene in water2008Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 10, nr 40, s. 6135-6143Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Solvation shell structure of a 7-piperidino-5,9-methanobenzo[8] annulene (PMA) in water has been investigated in ambient conditions using both molecular dynamics (MD) and Car-Parrinello molecular dynamics (CPMD) calculations. From the MD calculations, we find that this molecule exists in three major conformational states out of which two are in twist-boat forms and one in chair form. Due to the limited time scale accessible in CPMD simulations, we have studied all the three conformational states separately using CPMD. The molecular geometry, electronic charge distribution and solvation structure for all three forms are investigated. The stability order of the chair and twist-boat conformations in water solvent has been reversed when compared to the gaseous phase results and in the case of polar aprotic solvents (J. Org. Chem., 1999, 61, 5979). From the radial distribution function, we find that the solvent density around the chair form is significantly lower, which has to be directly related to the smaller solvent accessible area for this conformation and this is in complete agreement with earlier reports. Among the findings are that the solvation shell structure around the nitrogen atom in the chair form of PMA is considerably different from the open conformational forms or the twist-boat forms. The dipole moment for the closed form is found to be significantly larger when compared to the twist-boat forms.

  • 144.
    Murugan, N Arul
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Kongsted, J
    Rinkevicius, Zilvinas
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Aidas, Kestutis
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Mikkelsen, K V
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Hybrid density functional theory/molecular mechanics calculations of two-photon absorption of dimethylamino nitro stilbene in solution2011Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, nr 27, s. 12506-12516Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dimethylamino nitro stilbene (DANS) molecule is studied for exploring solvent effects on two-photon absorption using the quantum mechanical/molecular mechanical (QM/MM) response theory approach, where the quantum part is represented by density functional theory. We have explored the role of geometrical change of the chromophore in solution, the importance of taking a dynamical average over the sampled structures and the role of a granular representation of the polarization and electrostatic interactions with the classically described medium. The line shape function was simulated by the QM/MM technique thereby allowing for non-empirical prediction of the absolute two-photon cross section. We report a maximum in the TPA cross section for a medium of intermediate solvent polarity (i.e. in chloroform) and provide the grounds for an explanation of this effect which recently has been experimentally observed for a series of charge transfer species in solvents of different polarity. The calculations of absorption energies reproduce well the positive solvatochromic behavior of DANS and are in good agreement with experimental spectra available for the chloroform and DMSO solvents. In line with recent development of the QM/MM response technique for color modeling, we find this methodology to offer a versatile tool to predict and analyze two-photon absorption phenomena taking place within a medium.

  • 145.
    Natarajan Arul, Murugan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Jha, Prakash Chandra
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Solvation shell structure of cyclooctylpyranone in water solvent and its comparative structure, dynamics and dipole moment in HIV protease2009Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, nr 30, s. 6482-6489Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have investigated the solvation structure for cyclooctylpyranone (COP) in water solvent using force-field molecular dynamics (MD) and Car-Parrinello mixed quantum mechanics-molecular mechanics (CPMD) calculations. The MD calculations show that in water solvent COP can exist in two conformational states which differ with respect to the relative orientations of the three rings, namely phenyl, pyranone and cyclooctane. We report the existence of strong orientational preference for the water molecule in the first solvation shell and the orientational preference disappears for solvent molecules beyond the first solvation shell. In order to investigate the confinement effect on the structure, dynamics, charge distribution and dipole moment of COP, we have carried out MD and CPMD calculations for COP within HIV type-1 protease (PR). Interestingly, we do not see any conformational transitions for COP within the protein cavity and it remains as a single conformer. We do see a remarkable effect of confinement on few other torsional degrees of freedom such as gg to tg conformational shift for the propyl group of COP. However, the methyl group rotational dynamics remains similar in the water solvent and in the protein environment. Also, within the protein cavity, the COP molecule is more polarized when compared to water solvent. Static ab initio electronic structure calculations were performed on the COP molecule with varying torsional angle in order to investigate the angle dependence of the molecular volume and energy.

  • 146.
    Natarajan Arul, Murugan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Kongsted, Jacob
    Rinkevicius, Zilvinas
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Color modeling of protein optical probes2012Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, nr 3, s. 1107-1112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a strategy for modeling optical probes within heterogeneous environments of restricted dimension. The method is based on a multiphysics approach comprising sequential structure modeling by means of hybrid Car-Parrinello molecular dynamics and property modeling by means of quantum mechanics/molecular mechanics response theory. For demonstration we address the structural and optical properties of nile red within the beta-lacto globulin protein. We consider the cases with the probe situated on the surface or within the cavity of the protein, or embedded in a water solvent. We find the absorption properties of the probe to be highly dependent on its position relative to the protein. Structural rearrangements of the optical probe are found to contribute significantly to these environmental effects.

  • 147.
    Natarajan Arul, Murugan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Kongsted, Jacob
    Rinkevicius, Zilvinas
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Demystifying the solvatochromic reversal in Brooker's merocyanine dye2011Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, nr 4, s. 1290-1292Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Based on hybrid QM/MM simulation techniques, we rationalize the spectacular solvatochromic reversal behavior observed for a stilbazolium merocyanine (SM) called Brooker's merocyanine dye. This solvatochromic reversal is attributed to a change in the solute p-electron distribution from zwitterionic to neutral following the change in solvents from polar to non polar. Based on our calculations, we suggest that a polar solvent, like water, with larger relative permittivity is influential enough to bring the change in molecular structure from neutral to zwitterionic. Our results clearly indicate that SM exists in a neutral molecular structure in non polar solvents like trichloromethane and thereby we suggest that self-aggregation of SM may not occur in this solvent.

  • 148.
    Natarajan Arul, Murugan
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Zalesny, Robert
    Wroclaw Univ Sci & Technol, Fac Chem, Dept Phys & Quantum Chem, Wyb Wyspianskiego 27, PL-50370 Wroclaw, Poland..
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Centra, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Unusual binding-site-specific photophysical properties of a benzothiazole-based optical probe in amyloid beta fibrils2018Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 31, s. 20334-20339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optical imaging of amyloid fibrils serves as a cost-effective route for the diagnosis of Alzheimer-like conformational diseases. However, the challenge here is to optimize the binding affinity and photophysical properties of the optical imaging agents in a way specific to certain types of amyloids. In a few occasions it is shown that novel optical imaging agents can be designed to bind to a particular type of amyloid fibril with larger binding affinity and specificity. There is also a recent report on photoluminescent polythiophenes which display photophysical properties that can be used to distinguish the variants or subtypes of amyloids (J. Rasmussen et al., Proc. Natl. Acad. Sci. U. S. A., 2017, 114(49), 13018-13023). Based on a multiscale modeling approach, here, we report on the complementary aspect that the photophysical properties of a benzothiazole based optical probe (referred to as BTA-3) can be specific to the binding sites in the same amyloid fibrils and we attribute this to its varying electronic structure in different sites. As reported experimentally from competitive binding assay studies for many amyloid staining molecules and tracers, we also show multiple binding sites in amyloid fibrils for this probe. In particular, BTA-3 displayed a red-shift in its low-frequency absorption band only in site-4, a surface site of amyloid fibrils when compared to the spectra in water solvent. In the remaining sites, it exhibited a less significant blue shift for the same absorption band.

  • 149.
    Niga, Petru
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Johnson, C. Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Frey, Jeremy G.
    Rutland, Mark W.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Crown Ethers at the Aqueous Solution-Air Interface: 2. Electrolyte Effects, Ethylene Oxide Hydration and Temperature Behaviour2011Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, s. 7939-7947Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vibrational Sum Frequency Spectroscopy (VSFS) was employed to study adsorbing films of 4-Nitro Benzo-15-Crown-5 (NB15C5) and Benzo-15-Crown-5 (B15C5) at the aqueous solution–air interface. The surface of the solution is strongly influenced by the presence of crown ether species. Changes in the orientation of NB15C5 were monitored as a function of solution concentration, by targeting the ratio of peak intensities of the CN and NO2 vibrational modes. The water of hydration has also been probed as a function of crown concentration, salt concentration, and temperature. The latter study strongly suggests that the surface can be treated as a charged interface, and that the associated ordered water decreases with increasing ionic strength of the bulk solution.

  • 150.
    Niga, Petru
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    King, Wendy
    Hedberg, Jonas
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Johnson, C. Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Frey, Jeremy G.
    Rutland, Mark
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Crown Ethers at the Aqueous Solution-Air Interface: 1. Assignments and Surface Spectroscopy2011Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, nr 17, s. 7930-7938Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The surface of aqueous solutions of 4-Nitro Benzo-15-Crown-5 (NB15C5) and Benzo-15-Crown-5 (B15C5) has been studied using the surface sensitive technique vibrational sum frequency spectroscopy (VSFS). The NO, CN, COC and CH vibrational modes of these compounds at the air-water interface as well as OH vibrational modes of the surface water hydrating this compound have been targeted in order to obtain molecular information about arrangement and conformation of the adsorbed crown ether molecules at the air-water interface. The CH2 vibrational modes of crown ethers have been identified and found to be split due to interaction with ether oxygen. The spectra provide evidence for the existence of a protonated crown complex moiety at the surface leading to the appearance of strongly ordered water species. The interfacial water species are influenced by the resulting charged interface and by the strong Zundel polarizability due to tunneling of the proton species between equivalent sites within the crown ring.

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