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  • 1.
    Brumboiu, Iulia Emilia
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Prokopiou, G.
    Kronik, L.
    Brena, B.
    Valence electronic structure of cobalt phthalocyanine from an optimally tuned range-separated hybrid functional2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 4, article id 044301Article in journal (Refereed)
    Abstract [en]

    We analyse the valence electronic structure of cobalt phthalocyanine (CoPc) by means of optimally tuning a range-separated hybrid functional. The tuning is performed by modifying both the amount of short-range exact exchange (α) included in the hybrid functional and the range-separation parameter (γ), with two strategies employed for finding the optimal γ for each α. The influence of these two parameters on the structural, electronic, and magnetic properties of CoPc is thoroughly investigated. The electronic structure is found to be very sensitive to the amount and range in which the exact exchange is included. The electronic structure obtained using the optimal parameters is compared to gas-phase photo-electron data and GW calculations, with the unoccupied states additionally compared with inverse photo-electron spectroscopy measurements. The calculated spectrum with tuned γ, determined for the optimal value of α = 0.1, yields a very good agreement with both experimental results and with GW calculations that well-reproduce the experimental data.

  • 2.
    Brumboiu, Iulia
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. Korea Adv Inst Sci & Technol, Dept Chem, Daejeon 34141, South Korea..
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Norman, P.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Atomic photoionization cross sections beyond the electric dipole approximation2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 4, article id 044306Article in journal (Refereed)
    Abstract [en]

    A methodology is developed to compute photoionization cross sections beyond the electric dipole approximation from response theory, using Gaussian type orbitals and plane waves for the initial and final states, respectively. The methodology is applied to compute photoionization cross sections of atoms and ions from the first four rows of the periodic table. Analyzing the error due to the plane wave description of the photoelectron, we find kinetic energy and concomitant photon energy thresholds above which the plane wave approximation becomes applicable. The correction introduced by going beyond the electric dipole approximation increases with photon energy and depends on the spatial extension of the initial state. In general, the corrections are below 10% for most elements, at a photon energy reaching up to 12 keV. 2019 Author(s).

  • 3.
    Brumboiu, Iulia
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Haldar, Soumyajyoti
    Luder, Johann
    Eriksson, E.
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Herper, Heike C.
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Brena, Barbara
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Sanyal, Biplab
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Ligand Effects on the Linear Response Hubbard U: The Case of Transition Metal Phthalocyanines2019In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 123, no 14, p. 3214-3222Article in journal (Refereed)
    Abstract [en]

    It is established that density functional theory (DFT) + U is a better choice compared to DFT for describing the correlated electron metal center in organometallics. The value of the Hubbard U parameter may be determined from linear response, either by considering the response of the metal site alone or by additionally considering the response of other sites in the compound. We analyze here in detail the influence of ligand shells of increasing size on the U parameter calculated from the linear response for five transition metal phthalocyanines. We show that the calculated multiple-site U ligand atoms that are mainly responsible for this difference are is larger than the single-site U by as much as 1 eV and the ligand atoms that are mainly responsible for this difference are the isoindole nitrogen atoms directly bonded to the central metal atom. This suggests that a different U value may be required for computations of chemisorbed molecules compared to physisorbed and gas-phase cases.

  • 4.
    Zhang, T.
    et al.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;BIT, Sch Informat & Elect, Beijing 100081, Peoples R China..
    Brumboiu, Iulia
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. Korea Adv Inst Sci & Technol, Dept Chem, Daejeon 34141, South Korea..
    Lanzilotto, V.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Univ Roma La Sapienza, Dept Chem, Piazzale Aldo Moro 5, I-00185 Rome, Italy..
    Grazioli, C.
    Sincrotrone Trieste, Lab TASC, CNR, IOM, Trieste, Italy..
    Guarnaccio, A.
    CNR, ISM, Tito, Pz, Italy.;Trieste LD2 Unit, Trieste, Italy..
    Johansson, F. O. L.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Coreno, M.
    CNR, ISM, Tito, Pz, Italy.;Trieste LD2 Unit, Trieste, Italy..
    de Simone, M.
    Sincrotrone Trieste, Lab TASC, CNR, IOM, Trieste, Italy..
    Santagata, A.
    CNR, ISM, Tito, Pz, Italy.;Trieste LD2 Unit, Trieste, Italy..
    Brena, B.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Puglia, C.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Electronic structure modifications induced by increased molecular complexity: from triphenylamine to m-MTDATA2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 32, p. 17959-17970Article in journal (Refereed)
    Abstract [en]

    The starburst pi-conjugated molecule 4,4 ',4 ''-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (C57H48N4, m-MTDATA), based on triphenylamine (TPA) building blocks, is widely used in optoelectronic devices due to its good electron-donor characteristics. The electronic structure of m-MTDATA was investigated for the first time in the gas phase by means of PhotoElectron Spectroscopy (PES) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The combination of Density Functional Theory (DFT) calculations with the experimental spectra provides a comprehensive description of the molecular electronic structure. Moreover, by comparing the results with previous TPA measurements, we could shed light on how the electronic structure evolves when the molecular size is increased. We found that the C 1s photoelectron spectra of m-MTDATA and TPA are similar, due to the balance of the counter-acting effects of the electronegativity of the N atoms and the delocalization of the amine lone-pair electrons. In contrast, the increased number of N atoms (i.e. N lone pairs) in m-MTDATA determines a three-peak feature in the outermost valence binding energy region with strong contributions by the N 2p(z) orbitals. We also obtained a decrease of the HOMO-LUMO gap for m-MTDATA, which points to improved electron donating properties of m-MTDATA with respect to TPA.

  • 5. Zhang, T.
    et al.
    Brumboiu, Iulia
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Lanzilotto, V.
    Luder, J.
    Grazioli, C.
    Giangrisostomi, E.
    Ovsyannikov, R.
    Sass, Y.
    Bidermane, I.
    Stupar, M.
    de Simone, M.
    Coreno, M.
    Ressel, B.
    Pedio, M.
    Rudolf, P.
    Brena, B.
    Puglia, C.
    Conclusively Addressing the CoPc Electronic Structure: A Joint Gas-Phase and Solid-State Photoemission and Absorption Spectroscopy Study2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 47, p. 26372-26378Article in journal (Refereed)
    Abstract [en]

    The occupied and empty densities of states of cobalt phthalocyanine (CoPc) were investigated by photoelectron and X-ray absorption spectroscopies in the gas phase and in thin films deposited on a Au(111) surface. The comparison between the gas-phase results and density functional theory single-molecule simulations confirmed that the CoPc ground state is correctly described by the (2)A(1g) electronic configuration. Moreover, photon-energy-dependent valence photoemission spectra of both the gas phase and thin film confirmed the atomic character of the highest occupied molecular orbital as being derived from the organic ligand, with dominant contributions from the carbon atoms. Multiplet ligand-field theory was employed to simulate the Co L-edge X-ray absorption spectroscopy results.

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