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Berlin Brandenburg

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  • 1
    Language: English
    In: Physical chemistry chemical physics : PCCP, 14 July 2011, Vol.13(26), pp.12328-34
    Description: The ground state electronic structure of the high-temperature (HT) and the low-temperature (LT) phases of (EDO-TTF)(2)PF(6) is investigated using the embedded cluster approach in combination with the density functional method designed to describe the strong non-dynamic electron correlation. It is found that, in the HT phase, the unpaired electron spins located on pairs of neighbouring EDO-TTF molecules are antiferromagnetically coupled along the stacking direction with the Heisenberg exchange integral J = -655 cm(-1). In the LT phase, the unpaired spins located on the cationic EDO-TTF molecules are coupled antiferromagnetically with J values strongly alternating along the stacking axis of the crystal thus rendering it diamagnetic. The parameters of the extended Hubbard model are evaluated and the conductance properties of the two phases are estimated using these parameters. It is suggested to investigate the charge and spin excitations in the two phases of (EDO-TTF)(2)PF(6) with the use of angle-resolved photoemission spectroscopy.
    Keywords: Chemistry;
    ISSN: 14639076
    E-ISSN: 1463-9084
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  • 2
    In: Physical Chemistry Chemical Physics, 2011, Vol.13(26), pp.12328-12334
    Description: The ground state electronic structure of the high-temperature (HT) and the low-temperature (LT) phases of (EDO-TTF) 2 PF 6 is investigated using the embedded cluster approach in combination with the density functional method designed to describe the strong non-dynamic electron correlation. It is found that, in the HT phase, the unpaired electron spins located on pairs of neighbouring EDO-TTF molecules are antiferromagnetically coupled along the stacking direction with the Heisenberg exchange integral J = −655 cm −1 . In the LT phase, the unpaired spins located on the cationic EDO-TTF molecules are coupled antiferromagnetically with J values strongly alternating along the stacking axis of the crystal thus rendering it diamagnetic. The parameters of the extended Hubbard model are evaluated and the conductance properties of the two phases are estimated using these parameters. It is suggested to investigate the charge and spin excitations in the two phases of (EDO-TTF) 2 PF 6 with the use of angle-resolved photoemission spectroscopy.
    Keywords: Density-Functional Theory ; Referenced Kohn-Sham ; Basis-Sets ; Hartree-Fock ; Charge ; Elements ; Polarization ; Molecules ; Energies ; Solids;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 3
    Language: English
    In: The Journal of Chemical Physics, 28 September 2014, Vol.141(12)
    Description: Electron transfer in the ground and excited states of a model donor–acceptor (D–A) system is investigated using the single-reference and multi-reference density functional theory (DFT) methods. To analyze the results of the calculations, a simple two-site multi-reference model was derived that predicts a stepwise electron transfer in the S 0 state and a wave-like dependence of the S 1 electron transfer on the external stimulus. The standard single-reference Kohn-Sham (KS) DFT approach and the time-dependent DFT (TDDFT) method failed to describe the correct dependence of the S 0 and S 1 electron transfer on the external electric field applied along the donor–acceptor system. The multi-reference DFT approach, the spin-restricted ensemble-referenced KS (REKS) method, was able to successfully reproduce the correct behavior of the S 0 and S 1 electron transfer on the applied field. The REKS method was benchmarked against experimentally measured gas phase charge transfer excitations in a series of organic donor–acceptor complexes and displayed its ability to describe this type of electronic transitions with a very high accuracy, mean absolute error of 0.05 eV with the use of the standard range separated density functionals. On the basis of the calculations undertaken in this work, it is suggested that the non-adiabatic coupling between the S 0 and S 1 states may interfere with the electron transfer in a weakly coupled donor–acceptor system. It is also suggested that the electronic excitation of a D + –A − system may play a dual role by assisting the further electron transfer at certain magnitudes of the applied electric field and causing the backward transfer at lower electric field strengths.
    Keywords: Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 4
    In: Physical Chemistry Chemical Physics, 2010, Vol.13(1), pp.144-148
    Description: Magnetic properties of the TTF-CA molecular crystal below the neutral to ionic transition temperature are studied using the embedded cluster approach in combination with density functional theory. The calculated values of the Heisenberg exchange integral between the neighboring TTF and CA molecules stacked along the crystallographic axis a suggest that the ionic phase of the TTF-CA can be described as an alternating antiferromagnetic spin-1/2 Heisenberg chain with the exchange integral J = 1124 cm −1 and the alternation parameter δ = 0.46. Although the combination of ferroelectricity of the ionic phase with the antiferromagnetic ordering renders TTF-CA multiferroic (as predicted theoretically in G. Giovannetti et al. , Phys. Rev. Lett. , 2009, 103 , 266401), the large value of the alternation parameter should result in a nonmagnetic ground state of this phase. The dependence of the magnetic coupling parameters on the crystal structure is studied and the implications for experimental observation of magnetic properties of TTF-CA are discussed.
    Keywords: Alternations ; Antiferromagnetism ; Chains ; Crystals ; Ground State ; Integrals ; Magnetic Properties ; Order Disorder ; Miscellaneous Sciences (So);
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 5
    Language: English
    In: The journal of physical chemistry. A, 05 April 2012, Vol.116(13), pp.3481-6
    Description: Based on the normalized elimination of the small component relativistic formalism, a new approach to the calculation of hyperfine structure parameters of paramagnetic molecules is developed and implemented. The new method is tested in the calculation of the isotropic hyperfine structure constant for a series of open-shell molecules containing mercury. The results of calculations carried out in connection with ab initio methods of increasing complexity demonstrate the high accuracy of the formalism developed. In view of its computational simplicity, the new approach provides the basis for an efficient and accurate calculation of the HFS parameters of large molecules.
    Keywords: Chemistry;
    ISSN: 10895639
    E-ISSN: 1520-5215
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  • 6
    Language: English
    In: Journal of Organic Chemistry, April 18, 2014, Vol.79(8), pp.3587-3600
    Description: The article describes the rationalization of the effect of electron-withdrawing heteroatoms (such as a cationic nitrogen) on the topography and branching plane of mechanistically relevant conical intersections via analysis of model organic chromophores and synthesized rotary motors. Quantum chemical models of three distinct types of Schiff base rotary motors are designed and built using these concepts. One of the models having the indanylidenepyrroline framework has conical intersection structures consistent with an axial rotation.
    Keywords: Cations – Chemical Properties ; Cations – Research ; Quantum Chemistry – Research
    ISSN: 0022-3263
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: The Journal of organic chemistry, 18 April 2014, Vol.79(8), pp.3587-600
    Description: In the past, the design of light-driven single molecule rotary motors has been mainly guided by the modification of their ground-state conformational properties. Further progress in this field is thus likely to be achieved through a detailed understanding of light-induced dynamics of the system and the ways of modulating it by introducing chemical modifications. In the present theoretical work, the analysis of model organic chromophores and synthesized rotary motors is used for rationalizing the effect of electron-withdrawing heteroatoms (such as a cationic nitrogen) on the topography and branching plane of mechanistically relevant conical intersections. Such an analysis reveals how the character of rotary motion could be changed from a precessional motion to an axial rotational motion. These concepts are then used to design and build quantum chemical models of three distinct types of Schiff base rotary motors. One of these models, featuring the synthetically viable indanylidenepyrroline framework, has conical intersection structures consistent with an axial rotation not hindered by ground-state conformational barriers. It is expected that this type of motor should be capable of funneling the photon energy into specific rotary modes, thus achieving photoisomerization quantum efficiencies comparable to those seen in visual pigments.
    Keywords: Chemistry;
    ISSN: 00223263
    E-ISSN: 1520-6904
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  • 8
    Language: English
    In: Inorganic chemistry, 04 March 2013, Vol.52(5), pp.2497-504
    Description: 1,3-Benzenediamidoethanethiolatemercury [BDT-Hg or BD(S)-Hg] and its derivatives are investigated utilizing the Dirac exact relativistic normalized elimination of the small component method in connection with B3LYP, CCSD(T), and polarizable continuum calculations. It is shown that the chelating energy of BDT-Hg can be significantly increased by replacing sulfur with selenium or tellurium, thus leading to BD(Se)-Hg or BD(Te)-Hg. In this particular case, the chalcogenophilicity of mercury increases from S to Te because increasing the E-Hg bond lengths leads to a reduction of ring strain. Various possibilities of increasing the metal (M) chelating strength in BDT-M complexes are investigated, and suggestions for new chelating agents based on the BDT-M template are made.
    Keywords: Gravitation ; Quantum Theory ; Signal Processing, Computer-Assisted ; Environmental Pollutants -- Chemistry ; Mercury -- Isolation & Purification
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 9
    Language: English
    In: The Journal of Chemical Physics, 07 October 2012, Vol.137(13)
    Description: The dependence of the nuclear quadrupole coupling constants (NQCC) on the interaction between electrons and a nucleus of finite size is theoretically analyzed. A deviation of the ratio of the NQCCs obtained from two different isotopomers of a molecule from the ratio of the corresponding bare nuclear electric quadrupole moments, known as quadrupole anomaly, is interpreted in terms of the logarithmic derivatives of the electric field gradient at the nuclear site with respect to the nuclear charge radius. Quantum chemical calculations based on a Dirac-exact relativistic methodology suggest that the effect of the changing size of the Au nucleus in different isotopomers can be observed for Au-containing molecules, for which the predicted quadrupole anomaly reaches values of the order of 0.1%. This is experimentally detectable and provides an insight into the charge distribution of non-spherical nuclei.
    Keywords: Communications
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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  • 10
    Language: English
    In: The Journal of Chemical Physics, 07 July 2013, Vol.139(1)
    Description: A new algorithm for the two-component Normalized Elimination of the Small Component (2cNESC) method is presented and tested in the calculation of spin-orbit (SO) splittings for a series of heavy atoms and their molecules. The 2cNESC is a Dirac-exact method that employs the exact two-component one-electron Hamiltonian and thus leads to exact Dirac SO splittings for one-electron atoms. For many-electron atoms and molecules, the effect of the two-electron SO interaction is modeled by a screened nucleus potential using effective nuclear charges as proposed by Boettger [ Phys. Rev. B 62 , 7809 ( 2000 ) 10.1103/PhysRevB.62.7809 ] . The use of the screened nucleus potential for the two-electron SO interaction leads to accurate spinor energy splittings, for which the deviations from the accurate Dirac Fock-Coulomb values are on the average far below the deviations observed for other effective one-electron SO operators. For hydrogen halides HX (X = F, Cl, Br, I, At, and Uus) and mercury dihalides HgX 2 (X = F, Cl, Br, I) trends in spinor energies and SO splittings as obtained with the 2cNESC method are analyzed and discussed on the basis of coupling schemes and the electronegativity of X.
    Keywords: Articles
    ISSN: 0021-9606
    E-ISSN: 1089-7690
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