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  • 1.
    Al-Zoubi, Noura
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Medvedeva, A.
    Andersson, J.
    Nilson, G.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Tetragonality of carbon-doped ferromagnetic iron alloys: A first-principles study2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 1, p. 014112-Article in journal (Refereed)
    Abstract [en]

    Using density-functional theory in combination with the exact muffin-tin orbital (EMTO) method and coherent potential approximation, we investigate the alloying effect on the tetragonality of Fe-C solid solution forming the basis of steels. In order to assess the accuracy of our approach, first we perform a detailed study of the performance of the EMTO method for the Fe(16)C(1) binary system by comparing the EMTO results to those obtained using the projector augmented wave method. In the second step, we introduce different substitutional alloying elements (Al, Cr, Co, Ni) into the Fe matrix and study their impact on the structural parameters. We demonstrate that a small amount of Al, Co, and Ni enhances the tetragonal lattice ratio of Fe(16)C(1) whereas Cr leaves the ratio almost unchanged. The obtained trends are correlated with the single-crystal elastic parameters calculated for carbon-free alloys.

  • 2. Amft, Martin
    et al.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Influence of the cluster dimensionality on the binding behavior of CO and O(2) on Au(13)2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 2, p. 024312-Article in journal (Refereed)
    Abstract [en]

    We present an ab initio density functional theory study of the binding behavior of CO and O(2) molecules to two-and three-dimensional isomers of Au(13) in order to investigate the potential catalytic activity of this cluster towards low-temperature CO oxidation. First, we scanned the potential energy surface of Au(13) and studied the effect of spin-orbit coupling on the relative stabilities of the 21 isomers we identified. While spin-orbit coupling increases the stability of the three-dimensional more than the two-dimensional isomers, the ground state structure at 0 K remains planar. Second, we systematically studied the binding of CO and O(2) molecules onto the planar and three-dimensional structures lowest in energy. We find that the isomer dimensionality has little effect on the binding of CO to Au(13). O(2), on the other hand, binds significantly to the three-dimensional isomer only. The simultaneous binding of multiple CO molecules decreases the binding energy per molecule. Still, the CO binding remains stronger than the O(2) binding. We did not find a synergetic effect due to the co-adsorption of both molecular species. On the three-dimensional isomer, we find O(2) dissociation to be exothermic with an dissociation barrier of 1.44 eV.

  • 3.
    Amft, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Walle, L. E.
    Ragazzon, D.
    Borg, A.
    Uvdal, P.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Sandell, A.
    A Molecular Mechanism for the Water-Hydroxyl Balance during Wetting of TiO22013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 33, p. 17078-17083Article in journal (Refereed)
    Abstract [en]

    We show that the formation of the wetting layer and the experimentally observed continuous shift of the H2O-OH balance toward molecular water at increasing coverage on a TiO2(110) surface can be rationalized on a molecular level. The mechanism is based on the initial formation of stable hydroxyl pairs, a repulsive interaction between these pairs, and an attractive interaction with respect to water molecules. The experimental data are obtained by synchrotron radiation photoelectron spectroscopy and interpreted with the aid of density functional theory calculations and Monte Carlo simulations.

  • 4. Arapan, Sergiu
    et al.
    Simak, Sergei I.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Uppsala University, Sweden.
    Volume-dependent electron localization in ceria2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 12, article id 125108Article in journal (Refereed)
    Abstract [en]

    We have performed a numerical study of the process of electron localization in reduced ceria. Our results show that different localized charge distributions can be attained in a bulk system by varying the lattice parameter. We demonstrate that the effect of electron localization is mainly determined by lattice relaxation and an accurate account for the effects of electronic correlation is necessary to achieve localized charge distribution.

  • 5. Bondarenko, N.
    et al.
    Eriksson, O.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Hole bipolaron formation at (100) MgO/CaO epitaxial interface2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 12, p. 125118-Article in journal (Refereed)
    Abstract [en]

    Hole localization accompanying the formation of a cation vacancy in bulk MgO and CaO and at the (100) MgO/CaO interface is described using the Heyd-Scuseria-Ernzerhof hybrid functionals and DFT + U method. The ground state is found to be the O-1-O-1 bipolaronic configuration both in bulk oxides and at their interfaces. The ground-state magnetic configuration is a triplet, which has an energy only about 1-2 meV lower than that of the singlet state. The one-centered O-2-O-0 bipolaron was found to be metastable with its stability being enhanced at the interfaces compared to that in bulk oxides. Possible transition between different biplaronic configurations at the interface are analyzed for chosen configurations.

  • 6. Bondarenko, N.
    et al.
    Eriksson, O.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Polaron mobility in oxygen-deficient and lithium-doped tungsten trioxide2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 16, article id 165119Article in journal (Refereed)
    Abstract [en]

    Electron localization and polaron mobility in oxygen-deficient as well as Li-doped monoclinic tungsten trioxide have been studied in the adiabatic limit in the framework of density functional theory. We show that small polarons formed in the presence of oxygen vacancy prefer the bipolaronicW(5+)-W5+ configuration, whereas the W6+-W4+ configuration is found to be metastable. Our calculations suggest that bipolarons are tightly bound by the vacancy and therefore largely immobile. On the contrary, polarons formed as a result of Li intercalation can be mobile; the activation energy for polaron jumping in this case varies between 98 and 124 meV depending on the crystallographic direction. The formation of W5+-W5+ bipolarons in Li-WO3 is possible. When situated along [001] the bipolaronic configuration is 8 meV lower in energy than two separate W5+ polarons.

  • 7. Bondarenko, N.
    et al.
    Kvashnin, Y.
    Chico, J.
    Bergman, A.
    Eriksson, O.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Uppsala Univ, Sweden.
    Spin-polaron formation and magnetic state diagram in La-doped CaMnO32017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 22, article id 220401Article in journal (Refereed)
    Abstract [en]

    LaxCa1-xMnO3 (LCMO) has been studied in the framework of density functional theory (DFT) using Hubbard-U correction. We show that the formation of spin polarons of different configurations is possible in the G-type antiferromagnetic phase. We also show that the spin-polaron (SP) solutions are stabilized due to an interplay of magnetic and lattice effects at lower La concentrations and mostly due to the lattice contribution at larger concentrations. Our results indicate that the development of SPs is unfavorable in the C- and A-type antiferromagnetic phases. The theoretically obtained magnetic state diagram is in good agreement with previously reported experimental results.

  • 8. Chanda, Debabrata
    et al.
    Dobrota, Ana S.
    Hnat, Jaromir
    Sofer, Zdenek
    Pašti, Igor
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Skorodumova, Natalia, V
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Paidar, Martin
    Bouzek, Karel
    Investigation of electrocatalytic activity on a N-doped reduced graphene oxide surface for the oxygen reduction reaction in an alkaline medium2018In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 43, no 27, p. 12129-12139Article in journal (Refereed)
    Abstract [en]

    Today the search for new energy resources is a crucial topic for materials science. The development of new effective catalysts for the oxygen reduction reaction can significantly improve the performance of fuel cells as well as electrocatalytic hydrogen production. This study presents the scalable synthesis of nitrogen-doped graphene oxide for the oxygen reduction reaction. The combination of an ab initio theoretical investigation of the oxygen reduction reaction (ORR) mechanism and detailed electrochemical characterization allowed the identification of electrocatalytically active nitrogen functionalities. The dominant effect on electrocatalytic activity is the presence of graphitic and pyridinic nitrogen and also N-oxide functionalities. The overpotential of ORR for nitrogen-doped graphene oxide prepared by microwave-assisted synthesis outperformed the metal-doped graphene materials.

  • 9. Delczeg-Czirjak, E. K.
    et al.
    Edström, A.
    Werwinski, M.
    Rusz, J.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Eriksson, O.
    Stabilization of the tetragonal distortion of Fe chi Co1-chi alloys by C impurities: A potential new permanent magnet2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 14, p. 144403-Article in journal (Refereed)
    Abstract [en]

    We have analyzed by density functional theory calculations the structural and magnetic properties of Fe-Co alloys doped by carbon. In analogy with the formation of martensite in steels we predict that such a structure also forms for Fe-Co alloys in a wide range of concentrations. These alloys are predicted to have a stable tetragonal distortion, which in turn leads to an enhanced magnetocrystalline anisotropy energy of up to 0.75 MJ/m(3) and a saturated magnetization field of 1.9 T.

  • 10. Dobrota, Ana S.
    et al.
    Gutic, Sanjin
    Kalijadis, Ana
    Baljozovic, Milos
    Mentus, Slavko V.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Sweden.
    Pasti, Igor A.
    Stabilization of alkali metal ions interaction with OH-functionalized graphene via clustering of OH groups - implications in charge storage applications2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 63, p. 57910-57919Article in journal (Refereed)
    Abstract [en]

    Graphene synthesized by reduction of graphene oxide, depending on the degree of reduction, retains a certain amount of surface OH groups. Considering the surface OH groups/graphene layer system by means of density functional theory calculations, we evidenced the tendency of OH groups to cluster, resulting in enhanced system stability and no band gap opening. In the oxygen concentration range between 1.8 and 8.47 at%, with the addition of each new OH group, integral binding energy decreases, while differential binding energy shows the boost at even numbers of OH groups. Furthermore, we found that the clustering of OH groups over graphene basal plane plays a crucial role in enhancing the interactions with alkali metals. Namely, if alkali metal atoms interact with individual OH groups only, the interaction leads to an irreversible formation of MOH phase. When alkali atoms interact with clusters containing odd number of OH groups, a reversible transfer of an electron charge from the metal atom to the substrate takes place without OH removal. The strength of the interaction in general increases from Li to K. In an experimental investigation of a graphene sample which dominantly contains OH groups, we have shown that the trend in the specific interaction strength reflects to gravimetric capacitances measured in alkali metal chloride solutions. We propose that the charge stored in OH groups which interact with alkali metal cation and the pi electronic system of the graphene basal plane presents the main part of its pseudocapacitance.

  • 11. Dobrota, Ana S.
    et al.
    Pasti, Igor A.
    Mentus, Slavko V.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Functionalized graphene for sodium battery applications: the DFT insights2017In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 250, p. 185-195Article in journal (Refereed)
    Abstract [en]

    Considering the increasing interest in the use of graphene-based materials for energy conversion and storage applications, we have performed a DFT study of Na interaction with doped graphene, both in non-oxidized and oxidized forms. Oxidation seems to play the crucial role when it comes to the interaction of doped graphene materials with sodium. The dopants act as attractors of OH groups, making the material prone to oxidation, and therefore altering its affinity towards Na. In some cases, this can result in hydroxide or water formation - an irreversible change lethal for battery performance. Our results suggest that one should carefully control the oxidation level of doped graphene-based materials if they are to be used as sodium battery electrode materials as the optimal oxidation level depends on the dopant type.

  • 12. Dobrota, Ana S.
    et al.
    Pasti, Igor A.
    Mentus, Slavko V.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A DFT study of the interplay between dopants and oxygen functional groups over the graphene basal plane - implications in energy-related applications2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 12, p. 8530-8540Article in journal (Refereed)
    Abstract [en]

    Understanding the ways graphene can be functionalized is of great importance for many contemporary technologies. Using density functional theory calculations we investigate how vacancy formation and substitutional doping by B, N, P and S affect the oxidizability and reactivity of the graphene basal plane. We find that the presence of these defects enhances the reactivity of graphene. In particular, these sites act as strong attractors for OH groups, suggesting that the oxidation of graphene could start at these sites or that these sites are the most difficult to reduce. Scaling between the OH and H adsorption energies is found on both reduced and oxidized doped graphene surfaces. Using the O-2 molecule as a probe we show that a proper modelling of doped graphene materials has to take into account the presence of oxygen functional groups.

  • 13. Dobrota, Ana S.
    et al.
    Pasti, Igor A.
    Mentus, Slavko V.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    A general view on the reactivity of the oxygen-functionalized graphene basal plane2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 9, p. 6580-6586Article in journal (Refereed)
    Abstract [en]

    In this contribution we inspect the adsorption of H, OH, Cl and Pt on oxidized graphene using DFT calculations. The introduction of epoxy and hydroxyl groups on the graphene basal plane significantly alters its chemisorption properties, which can be attributed to the deformation of the basal plane and the type and distribution of these groups. We show that a general scaling relation exists between the hydrogen binding energies and the binding energies of other investigated adsorbates, which allows for a simple probing of the reactivity of oxidized graphene with only one adsorbate. The electronic states of carbon atoms located within the 2 eV interval below the Fermi level are found to be responsible for the interaction of the basal plane with the chosen adsorbates. The number of electronic states situated in this energy interval is shown to correlate with hydrogen binding energies.

  • 14. Dobrota, Ana S.
    et al.
    Pasti, Igor A.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Oxidized graphene as an electrode material for rechargeable metal-ion batteries - a DFT point of view2015In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 176, p. 1092-1099Article in journal (Refereed)
    Abstract [en]

    In line with a growing interest in the use of graphene-based materials for energy storage applications and active research in the field of rechargeable metal-ion batteries we have performed a DFT based computational study of alkali metal atoms (Li, Na and K) interaction with an oxidized graphene. The presence of oxygen surface groups (epoxy and hydroxyl) alters the chemisorption properties of graphene. In particular, we observe that the epoxy groups are redox active and enhance the alkali metal adsorption energies by a factor of 2 or more. When an alkali metal atom interacts with hydroxyl-graphene the formation of metal-hydroxide is observed. In addition to a potential boost of metal ion storage capability, oxygen functional groups also prevent the precipitation of the metal phase. By simulating lithiation/de-lithiation process on epoxy-graphenes, it was concluded that the oxidized graphene can undergo structural changes during battery operation. Our results suggest that the content and the type of oxygen surface groups should be carefully tailored to maximize the performance of metal-ion batteries. This is mainly related to the control of the oxidation level in order to provide enough active centers for metal ion storage while preserving sufficient electrical conductivity.

  • 15. Gutic, Sanjin J.
    et al.
    Dobrota, Ana S.
    Leetmaa, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden.
    Mentus, Slavko V.
    Pasti, Igor A.
    Improved catalysts for hydrogen evolution reaction in alkaline solutions through the electrochemical formation of nickel-reduced graphene oxide interface2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 20, p. 13281-13293Article in journal (Refereed)
    Abstract [en]

    H-2 production via water electrolysis plays an important role in hydrogen economy. Hence, novel cheap electrocatalysts for the hydrogen evolution reaction ( HER) are constantly needed. Here, we describe a simple method for the preparation of composite catalysts for H-2 evolution, consisting in simultaneous reduction of the graphene oxide film, and electrochemical deposition of Ni on its surface. The obtained composites (Ni@rGO), compared to pure electrodeposited Ni, show an improved electrocatalytic activity towards HER in alkaline media. We found that the activity of the Ni@rGO catalysts depends on the surface composition ( Ni vs. C mole ratio) and on the level of structural disorder of the rGO support. We suggest that HER activity is improved via H-ads spillover from the Ni particles to the rGO support, where quick recombination to molecular hydrogen is favored. A deeper insight into such a mechanism of H-2 production was achieved by kinetic Monte-Carlo simulations. These simulations enabled the reproduction of experimentally observed trends under the assumption that the support can act as a Hads acceptor. We expect that the proposed procedure for the production of novel HER catalysts could be generalized and lead to the development of a new generation of HER catalysts by tailoring the catalyst/support interface.

  • 16. Hellman, O.
    et al.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Simak, S. I.
    Charge Redistribution Mechanisms of Ceria Reduction2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 13, p. 135504-Article in journal (Refereed)
    Abstract [en]

    Charge redistribution at low oxygen vacancy concentrations in ceria have been studied in the framework of the density functional theory. We propose a model to approach the dilute limit using the results of supercell calculations. It allows one to reproduce the characteristic experimentally observed behavior of composition versus oxygen pressure dependency. We show that in the dilute limit the charge redistribution is likely to be driven by a mechanism different from the one involving electron localization on cerium atoms. We demonstrate that it can involve charge localization on light element impurities.

  • 17. Jovanović, A.
    et al.
    Dobrota, A. S.
    Rafailović, L. D.
    Mentus, S. V.
    Pašti, Igor
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Belgrade, Faculty of Physical Chemistry, Serbia.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; Humboldt University, Germany.
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. 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 correction2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 20, p. 13934-13943Article in journal (Refereed)
    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.

  • 18.
    Klarbring, Johan
    et al.
    Linkoping Univ, Dept Phys Chem & Biol IFM, SE-58183 Linkoping, Sweden..
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.
    Simak, Sergei I.
    Linkoping Univ, Dept Phys Chem & Biol IFM, SE-58183 Linkoping, Sweden..
    Finite-temperature lattice dynamics and superionic transition in ceria from first principles2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 10, article id 104309Article in journal (Refereed)
    Abstract [en]

    Ab initio molecular dynamics (AIMD) in combination with the temperature dependent effective potential (TDEP) method has been used to go beyond the quasiharmonic approximation and study the lattice dynamics in ceria, CeO2, at finite temperature. The results indicate that the previously proposed connection between the B-1u phonon mode turning imaginary and the transition to the superionic phase in fluorite structured materials is an artifact of the failure of the quasiharmonic approximation in describing the lattice dynamics at elevated temperatures. We instead show that, in the TDEP picture, a phonon mode coupling to the E-u mode prevents the B-1u mode from becoming imaginary. We directly observe the superionic transition at high temperatures in our AIMD simulations and find that it is initiated by the formation of oxygen Frenkel pairs (FP). These FP are found to form in a collective process involving simultaneous motion of two oxygen ions.

  • 19. Klarbring, Johan
    et al.
    Vekilova, Olga Yu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Nilsson, Johan O.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Simak, Sergei I.
    Ionic conductivity in Sm-doped ceria from first-principles non-equilibrium molecular dynamics2016In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 296, p. 47-53Article in journal (Refereed)
    Abstract [en]

    Sm-doped ceria is a prospective electrolyte material for intermediate-temperature solid-oxide fuel cells (IT-SOFC). Equi- librium ab initio molecular dynamics (AIMD) studies of oxygen ion diffusion in this material are currently impractical due to the rareness of diffusive events on the accessible timescale. To overcome this issue we have performed ab ini- tio non-equilibrium molecular dynamics calculations of Sm-doped ceria using the color-diffusion algorithm. Applying an external force field we have been able to increase the frequency of diffusive events over the simulation time, while keeping the physical mechanism of diffusion intact. We have investigated the temperature dependence of the maximum strength of the applied external field that could be used while maintaining the response of the system in a linear regime. This allows one to obtain the diffusivity at zero field. The bulk ionic conductivity has been calculated and found to match the experimental data well. We have also compared the description of the diffusion process by our method to previous findings and show that the migration mechanism and site preference of oxygen vacancies with respect to the Sm dopants is well reproduced. 

  • 20. Krivosheeva, A. V.
    et al.
    Shaposhnikov, V. L.
    Borisenko, V. E.
    Lazzari, J. -L
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Tay, B. K.
    Band gap modifications of two-dimensional defected MoS22015In: International Journal of Nanotechnology, ISSN 1475-7435, E-ISSN 1741-8151, Vol. 12, no 8-9, p. 654-662Article in journal (Refereed)
    Abstract [en]

    The changes in structural and electronic properties, occurring in one monolayer of MoS<inf>2</inf> at different concentrations of oxygen atoms doping and vacancies are investigated by means of ab initio computer simulation. The substitution of sulphur atoms by oxygen ones reduces the band gap for high concentrations only, transforming direct-gap semiconductor into an indirect one, whereas a smaller concentration of oxygen practically does not influence the gap. The presence of sulphur vacancies strongly reduces the band gap, leading to bands overlapping at high concentration and appearance of new bands at the gap region, which are determined by Mo 4d states with the mixture of S 3p states, at low concentrations.

  • 21.
    Leetmaa, M.a
    et al.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    KMCLib 1.1: Extended random number support and technical updates to the KMCLib general framework for kinetic Monte-Carlo simulations2015In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 196, p. 611-613Article in journal (Refereed)
    Abstract [en]

    We here present a revised version, v1.1, of the KMCLib general framework for kinetic Monte-Carlo (KMC) simulations. The generation of random numbers in KMCLib now relies on the C++11 standard library implementation, and support has been added for the user to choose from a set of C++11 implemented random number generators. The Mersenne-twister, the 24 and 48 bit RANLUX and a ’minimal-standard’ PRNG are supported. We have also included the possibility to use true random numbers via the C++11 std::random-device generator. This release also includes technical updates to support the use of an extended range of operating systems and compilers. New version program summary Program title: KMCLib v1.1 Catalogue identifier: AESZ-v1-1 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AESZ-v1-1.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 49,398 No. of bytes in distributed program, including test data, etc.: 1,536,855 Distribution format: tar.gz Programming language: Python and C++. Computer: Any computer that can run a C++11 compatible C++ compiler and a Python 2.7 interpreter. Operating system: Tested on Ubuntu 14.4 LTS, Ubuntu 12.4 LTS, CentOS 6.6, Mac OSX 10.10.3, Mac OSX 10.9.5 and Mac OSX 10.8.2 but should run on any system that can have a C++11 compatible C++ compiler and a Python 2.7 interpreter. Has the code been vectorized or parallelized?: Yes, with MPI. From one to hundreds of processors may be used depending on the type of input and simulation. RAM: From a few megabytes to several gigabytes depending on input parameters and the size of the system to simulate. Catalogue identifier of previous version: AESZ-v1-0 Journal reference of previous version: Comput. Phys. Comm. 185 (2014) 2340 Classification: 4.13, 16.13. External routines: To run the serial version of KMCLib no external libraries are needed other than the standard C++ runtime library and a Python 2.7 interpreter with support for numpy. For running the parallel version an MPI implementation is needed, such as e.g. MPICH from http://www.mpich.org or Open-MPI from http://www.open-mpi.org. SWIG (obtainable from http://www.swig.org/) and CMake (obtainable from http://www.cmake.org/) are both needed for building the backend module, while Sphinx (obtainable from http://sphinx-doc.org) is needed for building the documentation. CPPUNIT (obtainable from http://sourceforge.net/projects/cppunit/, also included in the KMCLib distribution) is needed for building the C++ unit tests Does the new version supersede the previous version?: Yes Nature of problem: Atomic scale simulation of slowly evolving dynamics is a great challenge in many areas of computational materials science and catalysis. When the rare-events dynamics of interest is orders of magnitude slower than the typical atomic vibrational frequencies a straight-forward propagation of the equations of motions for the particles in the simulation cannot reach time scales of relevance for modeling the slow dynamics. Solution method: KMCLib provides an implementation of the kinetic Monte Carlo (KMC) method that solves the slow dynamics problem by utilizing the separation of time scales between fast vibrational motion and the slowly evolving rare-events dynamics. Only the latter is treated explicitly and the system is simulated as jumping between fully equilibrated local energy minima on the slow-dynamics potential energy surface. Reasons for new version: The v1.1 revision increases the reliability and flexibility of the random number generation options in KMCLib, which is a central part of the KMC algorithm. The new release also comes with extended support for additional compilers and updates to the build system to simplify the installation procedure on some widely used platforms. Summary of revisions:Enough time has passed since the introduction of the <random> header in the C++ standard runtime library with the C++11 standard, that most installed compilers today have support to enable the use of C++11 specific language features in C+++. The <random> standard header comes with a set of well-defined pseudo random number generators (PRNG). Using standard library routines in favor of custom implementations has the obvious advantage of being more reliable and with guaranteed support over a longer time. From the v1.1 revision, KMCLib therefore relies on the C++11 standard library <random> header to produce pseudo-random numbers. This also makes it easier to enable support for several different PRNG:s for the user to choose from. From previously only supporting a Mersenne-twister implementation, KMCLib now has support for using the Mersenne-twister [1], the 24 and 48-bit RANLUX [2] generators, as well as a ’minimal-standard’ PRNG [3].For machines with a random device installed, KMCLib v1.1 can run simulations with true random numbers. This is enabled by using the std::random-device generator in C++. If the random device is properly installed the true random numbers are available to KMCLib out of the box and the user only needs to specify the use of the random device with an input flag in the same way as she chooses any of the available PRNG:s.The v1.1 revision includes major updates to the build system. The build system has no effect on the outcome of the simulations, but has a great impact on how easy it is to install the program. The Intel compiler is widely available on super computer clusters and support for this compiler widely extends the number of systems where KMCLib can be easily setup and run. The popularity of the Mac platform also makes smooth installation and compilation with clang desirable. With version v1.1 the make system for KMClib now includes support for the clang compiler on Mac and support for both the Intel compiler and the gcc compiler on Linux. See the reference manual for details of which versions of the operating systems and compilers have been tested.Restrictions: KMCLib implements the lattice KMC method and is as such, restricted to geometries that can be expressed on a grid in space. See the original paper describing KMCLib [4] for further details. Unusual features: KMCLib has been designed to be easily customized, to allow for user-defined functionality and integration with other codes. The user can define her own on-the-fly rate calculator via a Python API, so that site-specific elementary process rates, or rates depending on long-range interactions or complex geometrical features can easily be included. KMCLib also allows for on-the-fly analysis with user-defined analysis modules. KMCLib can keep track of individual particle movements and includes tools for mean square displacement analysis based on the algorithm described in Ref. [5], and is therefore particularly well suited for studying diffusion processes at surfaces and in solids. With the release of v1.1 KMCLib now supports several different pseudo random number generators, but can also, if a random device is installed on the machine, use true random numbers via the std::random-device generator. Additional comments: The full documentation of the program is distributed with the code and can also be found online at http://leetmaa.github.io/KMCLib/manual-v1.1/. Running time: From a few seconds to several days depending on the type of simulation and input parameters. References:M. Matsumoto and T. Nishimura, "Mersenne Twister: A 623- dimensionally equidistributed uniform pseudorandom number generator", ACM Trans. on Modeling and Computer Simulation, 8 (1998) 3.M. Lscher, "A portable high-quality random number generator for lattice field theory calculations", Computer Physics Communications, 79 (1994) 100110.S. K. Park, K. W. Miller and P K. Stockmeyer, "Technical correspondence", Communications of the ACM, 36 (1993) 105.M. Leetmaa and N. V. Skorodumova, "KMCLib: A general framework for lattice kinetic Monte Carlo (KMC) simulations", Computer Physics Communications, 185 (2014) 2340.M. Leetmaa and N. V. Skorodumova, "Mean square displacements with error estimates from non-equidistant time-step kinetic Monte Carlo simulations", Computer Physics Communications, 191 (2015) 119.

  • 22.
    Leetmaa, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Kinetic Monte Carlo modelling of ion diffusion. Example: Ceria2013In: EFC 2013 - Proceedings of the 5th European Fuel Cell Piero Lunghi Conference, 2013, p. 53-54Conference paper (Refereed)
    Abstract [en]

    Development of theoretical tools allowing us to study diffusion in solids at different scales is important for rational materials design. One of the effective approaches is a combination of Kinetic Monte Carlo technique with first principle electronic structure calculations. The KMClib program developed by us is a robust and flexible tool for studying diffusion, in particular, in ionconducting materials. The code has unique features such as on-thefly custom rate calculations, simulation of electrical bias and possibilities for on-the-fly analysis. It can be used in conjunction with ab initio calculations or just providing it with rates estimated from experiment or obtained in any other way. As an example of the code performance we present a simulation of oxygen diffusion in ceria.

  • 23.
    Leetmaa, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Department of Physics and Astronomy, Uppsala University.
    KMCLib: A general framework for lattice kinetic Monte Carlo (KMC) simulations2014In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 185, no 9, p. 2340-2349Article in journal (Refereed)
    Abstract [en]

    KMCLib is a general framework for lattice kinetic Monte Carlo (KMC) simulations. The program can handle simulations of the diffusion and reaction of millions of particles in one, two, or three dimensions, and is designed to be easily extended and customized by the user to allow for the development of complex custom KMC models for specific systems without having to modify the core functionality of the program. Analysis modules and on-the-fly elementary step diffusion rate calculations can be implemented as plugins following a well-defined API. The plugin modules are loosely coupled to the core KMCLib program via the Python scripting language. KMCLib is written as a Python module with a backend C++ library. After initial compilation of the backend library KMCLib is used as a Python module; input to the program is given as a Python script executed using a standard Python interpreter. We give a detailed description of the features and implementation of the code and demonstrate its scaling behavior and parallel performance with a simple one-dimensional A-B-C lattice KMC model and a more complex three-dimensional lattice KMC model of oxygen-vacancy diffusion in a fluorite structured metal oxide. KMCLib can keep track of individual particle movements and includes tools for mean square displacement analysis, and is therefore particularly well suited for studying diffusion processes at surfaces and in solids. Program summary Program title: KMCLib Catalogue identifier: AESZ_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AESZ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 49 064 No. of bytes in distributed program, including test data, etc.: 1 575 172 Distribution format: tar.gz Programming language: Python and C++. Computer: Any computer that can run a C++ compiler and a Python interpreter. Operating system: Tested on Ubuntu 12.4 LTS, CentOS release 5.9, Mac OSX 10.5.8 and Mac OSX 10.8.2, but should run on any system that can have a C++ compiler, MPI and a Python interpreter. Has the code been vectorized or parallelized?: Yes. From one to hundreds of processors depending on the type of input and simulation. RAM: From a few megabytes to several gigabytes depending on input parameters and the size of the system to simulate. Classification: 4.13, 16.13. External routines: KMCLib uses an external Mersenne Twister pseudo random number generator that is included in the code. A Python 2.7 interpreter and a standard C++ runtime library are needed to run the serial version of the code. For running the parallel version an MPI implementation is needed, such as e.g. MPICH from http://www.mpich.org or Open-MPI from http://www.open-mpi.org. SWIG (obtainable from http://www.swig.org/) and CMake (obtainable from http://www.cmake.org/) are needed for building the backend module, Sphinx (obtainable from http://sphinx-doc.org) for building the documentation and CPPUNIT (obtainable from http://sourceforge.net/projects/cppunit/) for building the C++ unit tests. Nature of problem: Atomic scale simulation of slowly evolving dynamics is a great challenge in many areas of computational materials science and catalysis. When the rare-events dynamics of interest is orders of magnitude slower than the typical atomic vibrational frequencies a straight-forward propagation of the equations of motions for the particles in the simulation cannot reach time scales of relevance for modeling the slow dynamics. Solution method: KMCLib provides an implementation of the kinetic Monte Carlo (KMC) method that solves the slow dynamics problem by utilizing the separation of time scales between fast vibrational motion and the slowly evolving rare-events dynamics. Only the latter is treated explicitly and the system is simulated as jumping between fully equilibrated local energy minima on the slow-dynamics potential energy surface. Restrictions: KMCLib implements the lattice KMC method and is as such restricted to geometries that can be expressed on a grid in space. Unusual features: KMCLib has been designed to be easily customized, to allow for user-defined functionality and integration with other codes. The user can define her own on-the-fly rate calculator via a Python API, so that site-specific elementary process rates, or rates depending on long-range interactions or complex geometrical features can easily be included. KMCLib also allows for on-the-fly analysis with user-defined analysis modules. KMCLib can keep track of individual particle movements and includes tools for mean square displacement analysis, and is therefore particularly well suited for studying diffusion processes at surfaces and in solids. Additional comments: The full documentation of the program is distributed with the code and can also be found at http://www.github.com/leetmaa/KMCLib/manual Running time: From a few seconds to several days depending on the type of simulation and input parameters.

  • 24.
    Leetmaa, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Uppsala University, Sweden.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Uppsala University, Sweden.
    Mean square displacements with error estimates from non-equidistant time-step kinetic Monte Carlo simulations2015In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 191, p. 119-124Article in journal (Refereed)
    Abstract [en]

    We present a method to calculate mean square displacements (MSD) with error estimates from kinetic Monte Carlo (KMC) simulations of diffusion processes with non-equidistant time-steps. An analytical solution for estimating the errors is presented for the special case of one moving particle at fixed rate constant. The method is generalized to an efficient computational algorithm that can handle any number of moving particles or different rates in the simulated system. We show with examples that the proposed method gives the correct statistical error when the MSD curve describes pure Brownian motion and can otherwise be used as an upper bound for the true error.

  • 25. Migas, D. B.
    et al.
    Bogorodz, V. O.
    Filonov, A. B.
    Borisenko, V. E.
    Skorodumova, N. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Quasi-2D silicon structures based on ultrathin Me2Si (Me = Mg, Ca, Sr, Ba) films2018In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 670, p. 51-57Article in journal (Refereed)
    Abstract [en]

    By means of ab initio calculations with hybrid functionals we show a possibility for quasi-2D silicon structures originated from semiconducting Mg2Si, Ca2Si, Sr2Si and Ba2Si silicides to exist. Such a 2D structure is similar to the one of transition metal chalcogenides where silicon atoms form a layer in between of metal atoms aligned in surface layers. These metal surface atoms act as pseudo passivation species stabilizing crystal structure and providing semiconducting properties. Considered 2D Mg2Si, Ca2Si, Sr2Si and Ba2Si have band gaps of 1.14 eV, 0.69 eV, 0.33 eV and 0.19 eV, respectively, while the former one is also characterized by a direct transition with appreciable oscillator strength. Electronic states of the surface atoms are found to suppress an influence of the quantum confinement on the band gaps. Additionally, we report Sr2Si bulk in the cubic structure to have a direct band gap of 0.85 eV as well as sizable oscillator strength of the first direct transition. 

  • 26. Migas, D. B.
    et al.
    Filonov, A. B.
    Borisenko, V. E.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Department of Physics and Astronomy, Uppsala University, Sweden.
    Orientation effects in morphology and electronic properties of anatase TiO2 one-dimensional nanostructures. II. Nanotubes2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 20, p. 9490-9498Article in journal (Refereed)
    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.

  • 27. Migas, D. B.
    et al.
    Shaposhnikov, V. L.
    Borisenko, V. E.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    The Surface Energy and Band Structure of gamma-WO3 Thin Films2017In: Science of Advanced Materials, ISSN 1947-2935, E-ISSN 1947-2943, Vol. 9, no 3-4, p. 469-474Article in journal (Refereed)
    Abstract [en]

    By means of ab initio calculations we demonstrate sizable anisotropy in surface energy of the gamma-WO3 (001), (010) and (100) surfaces. The (001) surface has the smallest surface energy followed by the (010) and (100) surfaces. Their surface band structures are characterized by dispersion of bands near the gap region and by band-gap values similar to the ones of the bulk. The role of surface atoms in stabilizing the band gap is revealed. Variations in the position of the Fermi level are traced with respect to the different surface reconstructions.

  • 28. Migas, Dmitri B.
    et al.
    Filonov, Andrew B.
    Borisenko, Victor E.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Orientation effects in morphology and electronic properties of anatase TiO2 one-dimensional nanostructures. I. Nanowires2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 20, p. 9479-9489Article in journal (Refereed)
    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.

  • 29.
    Nilsson, Johan O.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Leetmaa, Mikael
    Vekilova, Olga Yu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Simak, Sergei I.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Oxygen diffusion in ceria doped with rare-earth elementsManuscript (preprint) (Other academic)
  • 30.
    Nilsson, Johan O.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Leetmaa, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vekilova, Olga Yu.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden.
    Simak, Sergei I.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden.
    Oxygen diffusion in ceria doped with rare-earth elements2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, p. 13723-13730Article in journal (Refereed)
    Abstract [en]

    We examine the effects of the dopant type and the dopant distribution on the ion diffusion in ceria doped with rare-earth elements (Pr, Nd, Pm, Sm, Eu, and Gd). Diffusion is simulated by means of a Kinetic Monte Carlo method using input transition rates derived from diffusion barriers calculated in the framework of density functional theory (DFT). Based on diffusion simulations, we discuss the characteristics of the dopants in terms of the diffusion barriers, and study oxygen ion trajectories for different dopants and distributions. Our simulations show a trend of increasing ion diffusivity with increasing atomic number for all distributions.

  • 31.
    Nilsson, Johan O.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Leetmaa, Mikael
    Vekilova, Olga Yu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Simak, Sergei I.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Statistical error in simulations of Poisson processes: Example of diffusion in solids2016In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 94, no 8, article id 085206Article in journal (Refereed)
    Abstract [en]

    Simulations of diffusion in solids often produce poor statistics of diffusion events. We present an analytical expression for the statistical error in ion conductivity obtained in such simulations. The error expression is not restricted to any computational method in particular, but valid in the context of simulation of Poisson processes in general. This analytical error expression is verified numerically for the case of Gd-doped ceria by running a large number of kinetic Monte Carlo calculations. 

  • 32.
    Nilsson, Johan O.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Leetmaa, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wang, B.
    Zguns, Pjotrs
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Pašti, I.
    Sandell, A.
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Modeling Kinetics of Water Adsorption on the Rutile TiO2 (110) Surface: Influence of Exchange-Correlation Functional2018In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 255, no 3, article id 1700344Article in journal (Refereed)
    Abstract [en]

    The accuracy of the theoretical description of materials properties in the framework of density functional theory (DFT) inherently depends on the exchange-correlation (XC) functional used in the calculations. Here we investigate the influence of the choice of a XC functional (PBE, RPBE, PW91, and PBE0) on the kinetics of the adsorption, diffusion and dissociation of water on the rutile TiO2(110) surface using a combined Kinetic Monte Carlo (KMC) – DFT approach, where the KMC simulations are based on the barriers for the aforementioned processes calculated with DFT. We also test how the adsorption energy of intact and dissociated water molecules changes when dispersion interactions are included into the calculations. We consider the beginning of the water layer formation varying coverage up to 0.2 monolayer (ML) at temperatures up to 180 K. We demonstrate that the dynamics of the simulated water–titania system is extremely sensitive to the choice of the XC functional.

  • 33.
    Nilsson, Johan O.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Leetmaa, Mikael
    Wang, Baochang
    Zguns, Pjotrs A.
    Sandell, Anders
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kinetics of water adsorption on the rutile TiO2(110) surfaceManuscript (preprint) (Other academic)
  • 34.
    Nilsson, Johan O.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vekilova, Olga Yu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hellman, Olle
    Klarbring, Johan
    Simak, Sergei I.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ionic conductivity in Gd-doped CeO2: Ab initio color-diffusion nonequilibrium molecular dynamics study2016In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 93, no 2, article id 024102Article in journal (Refereed)
    Abstract [en]

    A first-principles nonequilibrium molecular dynamics (NEMD) study employing the color-diffusion algorithm has been conducted to obtain the bulk ionic conductivity and the diffusion constant of gadolinium-doped cerium oxide (GDC) in the 850-1150 K temperature range. Being a slow process, ionic diffusion in solids usually requires simulation times that are prohibitively long for ab initio equilibrium molecular dynamics. The use of the color-diffusion algorithm allowed us to substantially speed up the oxygen-ion diffusion. The key parameters of the method, such as field direction and strength as well as color-charge distribution, have been investigated and their optimized values for the considered system have been determined. The calculated ionic conductivity and diffusion constants are in good agreement with available experimental data.

  • 35.
    Noura, Al-Zoubi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Medvedeva, A.
    Andersson, J.
    Nilson, G.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Tetragonlity of carbon-doped ferromagnetic iron alloys: a first-priniciples studyIn: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453Article in journal (Other academic)
  • 36. Nowakowska, Sylwia
    et al.
    Mazzola, Federico
    Alberti, Mariza N.
    Song, Fei
    Voigt, Tobias
    Nowakowski, Jan
    Wackerlin, Aneliia
    Wackerlin, Christian
    Wiss, Jerome
    Schweizer, W. Bernd
    Broszio, Max
    Polley, Craig
    Leandersson, Mats
    Fatayer, Shadi
    Ivas, Toni
    Baljozovic, Milos
    Mousavi, S. Fatemeh
    Ahsan, Aisha
    Nijs, Thomas
    Popova, Olha
    Zhang, Jun
    Muntwiler, Matthias
    Thilgen, Carlo
    Stohr, Meike
    Pasti, Igor A.
    Skorodumova, Natalia V
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Diederich, Francois
    Wells, Justin
    Jung, Thomas A.
    Adsorbate-Induced Modification of the Confining Barriers in a Quantum Box Array2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 1, p. 768-778Article in journal (Refereed)
    Abstract [en]

    Quantum devices depend on addressable elements, which can be modified separately and in their mutual interaction. Self-assembly at surfaces, for example, formation of a porous (metal-) organic network, provides an ideal way to manufacture arrays of identical quantum boxes, arising in this case from the confinement of the electronic (Shockley) surface state within the pores. We show that the electronic quantum box state as well as the interbox coupling can be modified locally to a varying extent by a selective choice of adsorbates, here C-60, interacting with the barrier. In view of the wealth of differently acting adsorbates, this approach allows for engineering quantum states in on-surface network architectures.

  • 37. Pasti, Igor A.
    et al.
    Baljozovic, Milos R.
    Granda-Marulanda, Laura P.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Bimetallic dimers adsorbed on a defect-free MgO(001) surface: bonding, structure and reactivity2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 15, p. 9666-9679Article in journal (Refereed)
    Abstract [en]

    A large number of computational studies have been devoted to the investigation of monometallic clusters supported by MgO. However, in practice, catalysis shows that multicomponent catalytic systems often win in catalytic performance over single component systems. In this study, the geometrical and electronic structure, stability and chemisorption properties of M1M2 metal dimers (M1, M2 = Ru, Rh, Pd, Ir, Pt) supported by defect free MgO(001) have been investigated in the framework of density functional theory. The oxygen sites of MgO(001) are the preferred adsorption sites for all the studied clusters, the majority of them adsorbing parallel to the surface with metal atoms attached to two surface oxygen atoms. The energetics of M1M2 + MgO(001) formation shows that the adsorption complexes are stable and benefit from metal-oxygen and metal-metal interaction. The chemisorption properties of Pd and Pt atoms in PdM2 and PtM2 dimers are studied using CO as a probe molecule. A linear relationship between the CO chemisorption and the d-band center position of the reacting atom in the dimer is observed, extending the d-band center model to the case of highly under-coordinated metal atoms supported by a non-conductive material.

  • 38. Pasti, Igor A.
    et al.
    Baljozovic, Milos
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Uppsala Univ, Dept Phys & Astron, Sweden.
    Adsorption of nonmetallic elements on defect-free MgO(001) surface - DFT study2015In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 632, p. 39-49Article in journal (Refereed)
    Abstract [en]

    Adsorption of 11 non-metals (H, B, C, N, O, F, Si, P, S, Cl and Br) on defect-free MgO(001) surface was investigate using DFT approach. Adsorption energies were found to be between -0.56 eV (hydrogen adsorption) and -2.63 eV (carbon adsorption). Charge transfer from substrate to adsorbate was observed to follow the periodicity in the Periodic Table of Elements, as increases from left to right and decreases from top to bottom. All investigated adsorbates prefer oxygen sites on MgO surface. The analysis of adsorbate-MgO(001) electronic structure suggested that the electronic structure of the O adsorption center and adsorbate atom is molecule-like and there is no strong interaction with MgO electronic bands. Based on the obtained dataset for adsorption energies of selected non-metallic adsorbates (X) the reactivity of MgO towards the bond cleavage in the cases of X-X, H-X and HO-X bonds was discussed. Obtained results point to weak reactivity of MgO(001) towards atomic adsorption and low activity for bond cleavage. However, these results can be used as a starting point for the functionalization of MgO, particularly in the cases where bond cleavage activity and surface-mediated stabilization of dissociation products are desired.

  • 39.
    Pasti, Igor A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Tunable reactivity of supported single metal atoms by impurity engineering of the MgO(001) support2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 9, p. 6337-6346Article in journal (Refereed)
    Abstract [en]

    Development of novel materials may often require a rational use of high price components, like noble metals, in combination with the possibility to tune their properties in a desirable way. Here we present a theoretical DFT study of Au and Pd single atoms supported by doped MgO(001). By introducing B, C and N impurities into the MgO(001) surface, the interaction between the surface and the supported metal adatoms can be adjusted. Impurity atoms act as strong binding sites for Au and Pd adatoms and can help to produce highly dispersed metal particles. The reactivity of metal atoms supported by doped MgO(001), as probed by CO, is altered compared to their counterparts on pristine MgO(001). We find that Pd atoms on doped MgO(001) are less reactive than on perfect MgO(001). In contrast, Au adatoms bind CO much more strongly when placed on doped MgO(001). In the case of Au on N-doped MgO(001) we find that charge redistribution between the metal atom and impurity takes place even when not in direct contact, which enhances the interaction of Au with CO. The presented results suggest possible ways for optimizing the reactivity of oxide supported metal catalysts through impurity engineering.

  • 40.
    Pasti, Igor A.
    et al.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Jovanovic, Aleksandar
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;CEST Kompetenzzentrum Elektrochem Oberfiachentecn, Viktor Kaplan Str 2,Sect A, A-2700 Wiener Neustadt, Austria..
    Dobrota, Ana S.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia..
    Mentus, Slavko V.
    Univ Belgrade, Fac Phys Chem, Studentski Trg 12-16, Belgrade 11158, Serbia.;Serbian Acad Arts & Sci, Knez Mihajlova 35, Belgrade 11000, Serbia..
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Dept Phys & Astron, POB 516, S-75120 Uppsala, Sweden..
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Dept Phys & Astron, POB 516, S-75120 Uppsala, Sweden..
    Atomic adsorption on pristine graphene along the Periodic Table of Elements - From PBE to non-local functionals2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 436, p. 433-440Article in journal (Refereed)
    Abstract [en]

    The understanding of atomic adsorption on graphene is of high importance for many advanced technologies. Here we present a complete database of the atomic adsorption energies for the elements of the Periodic Table up to the atomic number 86 (excluding lanthanides) on pristine graphene. The energies have been calculated using the projector augmented wave (PAW) method with PBE, long-range dispersion interaction corrected PBE (PBE+D2, PBE+D3) as well as non-local vdW-DF2 approach. The inclusion of dispersion interactions leads to an exothermic adsorption for all the investigated elements. Dispersion interactions are found to be of particular importance for the adsorption of low atomic weight earth alkaline metals, coinage and s-metals (11th and 12th groups), high atomic weight p-elements and noble gases. We discuss the observed adsorption trends along the groups and rows of the Periodic Table as well some computational aspects of modelling atomic adsorption on graphene.

  • 41. Pasti, Igor A.
    et al.
    Jovanovic, Aleksandar
    Dobrota, Ana S.
    Mentus, Slavko V.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Atomic adsorption on graphene with a single vacancy: systematic DFT study through the periodic table of elements2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 2, p. 858-865Article in journal (Refereed)
    Abstract [en]

    Vacancies in graphene present sites of altered chemical reactivity and open possibilities to tune graphene properties by defect engineering. The understanding of chemical reactivity of such defects is essential for successful implementation of carbon materials in advanced technologies. We report the results of a systematic DFT study of atomic adsorption on graphene with a single vacancy for the elements of rows 1-6 of the periodic table of elements (PTE), excluding lanthanides. The calculations have been performed using the PBE, long-range dispersion interaction-corrected PBE (PBE+D2 and PBE+D3) and non-local vdW-DF2 functionals. We find that most elements strongly bind to the vacancy, except for the elements of groups 11 and 12, and noble gases, for which the contribution of dispersion interaction to bonding is most significant. The strength of the interaction with the vacancy correlates with the cohesive energy of the elements in their stable phases: the higher the cohesive energy is, the stronger bonding to the vacancy can be expected. As most atoms can be trapped at the SV site we have calculated the potentials of dissolution and found that in most cases the metals adsorbed at the vacancy are more "noble" than they are in their corresponding stable phases.

  • 42. Pasti, Igor A.
    et al.
    Leetmaa, Mikael
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univiversity, Sweden.
    General principles for designing supported catalysts for hydrogen evolution reaction based on conceptual Kinetic Monte Carlo modeling2016In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, no 4, p. 2526-2538Article in journal (Refereed)
    Abstract [en]

    Rational catalyst design presents one of the main paradigms in the contemporary materials science. Although the electronic structure calculations can be used to search for possible candidates, realistic supported catalysts are difficult to address in this way. In this contribution we use conceptual model of the supported hydrogen evolution reaction (HER) catalyst and investigate possible processes using Kinetic Monte Carlo simulations. In specific, we look at the possibility to boost H-2 production by the H spillover to the support and the tailoring of the catalyst deposit. Different scenarios were considered depending on the nature of the HER rate determining step (RDS) on the catalyst surface and the effects of the rates of elementary processes, catalyst dispersion and morphology are analyzed. Metals with low affinity towards hydrogen should be used as catalyst supports, while H spillover can boost H-2 production if Tafel or Heyrovsky reaction is the RDS on the catalyst surface. However, this can be achieved only if the catalyst dispersion is high, while the support has to act as a Hads acceptor and enable fast Hads recombination. General instructions for the choice of the catalystlsupport combination can be used to design new advanced HER catalysts. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

  • 43. Pasti, Igor A.
    et al.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Uppsala University, Sweden.
    Mentus, Slavko V.
    Theoretical studies in catalysis and electrocatalysis: from fundamental knowledge to catalyst design2015In: Reaction Kinetics, Mechanisms and Catalysis, ISSN 1878-5190, E-ISSN 1878-5204, Vol. 115, no 1, p. 5-32Article in journal (Refereed)
    Abstract [en]

    Catalytic processes are an indispensable part of a large number of contemporary technologies that stimulate a constant research and development effort in the field. Computational methods represent a valuable tool to investigate crucial steps of catalytic cycles able to reveal the main characteristics of a catalyst and provide a basis for the design of materials with superior catalytic activity. This review is focused on the recent advances in density functional theory studies of the interactions of reactive species and intermediates with solid surfaces. As examples, we discuss the catalysts for the CO oxidation and electrocatalysis of H-2 and O-2 electrode reactions. We demonstrate how the theoretical modelling can contribute to the understanding of catalytic processes and help to design new catalysts and electrocatalysts.

  • 44. Pašti, I. A.
    et al.
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Uppsala University, Sweden.
    Structural, electronic, magnetic and chemical properties of B-, C- and N-doped MgO(001) surfaces2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 1, p. 426-435Article in journal (Refereed)
    Abstract [en]

    Doping of simple oxide materials can give rise to new exciting physical and chemical properties and open new perspectives for a variety of possible applications. Here we use density functional theory calculations to investigate the B-, C- and N-doped MgO(001) surfaces. We have found that the investigated dopants induce magnetization of the system amounting to 3, 2 and 1 μB for B, C and N, respectively. The dopants are found to be in the X2- state and tend to segregate to the surface. These impurity sites also present the centers of altered chemical reactivity. We probe the chemisorption properties of the doped MgO(001) surfaces with the CO molecule and atomic O. The adsorption of CO is much stronger on B- and C-doped MgO(001) compared to pure MgO(001) as the impurity sites serve as potent electron donors. The situation is similar to the case of atomic oxygen, for which we find the adsorption energy of -8.78 eV on B-doped MgO(001). The surface reactivity changes locally around the dopant atom, which is mainly restricted to its first coordination shell. The presented results suggest doped MgO as a versatile multifunctional material with possible use as an adsorbent or a catalyst.

  • 45.
    Ruban, Andrei V.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Belonoshko, Anatoly B.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Impact of magnetism on Fe under Earth's core conditions2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 1, p. 014405-Article in journal (Refereed)
    Abstract [en]

    Using a microscopic phenomenological model for longitudinal spin fluctuations (LSFs) based on density functional theory calculations, we demonstrate that under the Earth's core conditions (P approximate to 360 GPa, T approximate to 6000 K), Fe acquires substantial local magnetic moment, up to 1.3 mu(B), for different crystal structure modifications. We demonstrate that the LSFs produce a substantial effect on the magnetic and thermodynamic properties of iron, in particular, its equilibrium volume under solid Earth's core conditions.

  • 46.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Theoretical design of ceria-based electrolyte materials2011In: EFC 2011 - Proceedings of the 4th European Fuel Cell Piero Lunghi Conference and Exhibition, 2011, p. 61-62Conference paper (Refereed)
    Abstract [en]

    Recent method development and increasing computer power have made ab initio methods of computational physics a robust, complimentary tool of modern materials research. Here we discuss how these methods can be used to understand some basic mechanisms determining the ion mobility in ceria-based electrolyte materials and to predict compositions with improved ion conductivity as well as to suggest new doping strategies.

  • 47.
    Wang, Baochang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Leetmaa, Mikael
    Ragazzon, Davide
    Walle, Lars Erik
    Borg, Anne
    Uvdal, Per
    Sandell, Anders
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Kinetics of water adsorption on TiO2(110)Manuscript (preprint) (Other academic)
  • 48.
    Wang, Baochang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Division of Materials Theory, Department of Physics and Astronomy, Uppsala University, Sweden.
    Structure and optical properties of (CdSxSe1-x) 42 nanoclusters2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 27, p. 13956-13963Article in journal (Refereed)
    Abstract [en]

    The structures of the (CdS)(42), (CdSe)(42), Cd42Se32S10, Cd42Se22S20, and Cd42Se10S32 clusters have been determined using the simulated annealing method. Factors influencing the band gap value have been analysed. We show that the gap is most significantly reduced when strongly under coordinated atoms are present on the surface of the nanoclusters. In addition, the band gap depends on the S concentration as well as on the distribution of the S and Se atoms in the clusters. We present the optical absorption spectra calculated with BSE and RPA methods based on the GW corrected quasiparticle energies. Strong electron-hole coupling is observed for all the clusters, shifting the calculated RPA onset of optical absorption to lower energies. The absorption edge is shifted to higher photon energies as S concentration increases. The calculated energy separation of the first bright exciton and first dark exciton increases with S concentration.

  • 49. Wang, Richard B.
    et al.
    Koerbel, Sabine
    Saha, Santanu
    Botti, Silvana
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Uppsala University, Sweden.
    Structure and Optical Properties of Small (TiO2)(n) Nanoparticles, n=21-242017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 17, p. 9528-9536Article in journal (Refereed)
    Abstract [en]

    Recently, nanostructured TiO2 ("black TiO2") has been discovered to absorb visible light, which makes, it an efficient material for water splitting. Hydrogenization has been proposed to be at the origin of this beneficial electronic structure of black TiO2. Here, we investigate, using ab initio methods, alternative mechanisms related to structure modifications in nanoclusters that could be responsible for absorption in the visible range. To that end, we apply a combination of computational structure prediction using simulated annealing and minima-hopping methods based on density-functional theory to predict low-energy configurations and time-dependent density-functional theory (TDDFT) using a hybrid functional with optimized Hartree Fock content to obtain optical absorption edges.

  • 50. Wessel, Michael
    et al.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Adhesion of the TiN/Fe interface with point defects from first principles2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 1, p. 014905-Article in journal (Refereed)
    Abstract [en]

    We have investigated the bonding and adhesion of the TiN(001)/fcc-Fe(111) interface with and without defects using density functional theory. Substitutions in Fe, vacancies and impurities in TiN as well as the influence of vertical stress are studied. The performed bonding analysis shows that the main interaction between Fe and TiN originated from the Fe-N bonding, regardless of the specific set-up. For the ideal TiN(001)/fcc-Fe(111) interface, a complete separation of the interface is preferred to any transfer of iron atoms to the TiN surface. The presence of Ti and N vacancies or alloying elements at the interface further promotes this trend. Application of stress to the system lowers sliding barriers along the Tin/Fe interface.

12 1 - 50 of 55
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