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1.
B. N. Plakhutin G. M. Zhidomirov A. V. Arbuznikov 《International journal of quantum chemistry》1992,41(2):311-325
We derived the necessary conditions to which the vector coupling coefficients (VCC ) a and b describing atomic L,S-multiplets of the configurations dN (1 ≤ N ≤ 9), should satisfy. Special attention is paid to the states of non-Roothaan type for which VCC depend on the choice of degenerate d-orbitals basis set determined within the accuracy up to an orthogonal transformation u. It is shown that for such states the direct sum of matrices ‖a‖ and ‖b‖ must be the non-symmetric matrix. Obtained VCC were used for the ab initio calculations (basis set (14s9p5d)/[8s4p2d] from [15]) on first-row transition atoms (from Sc to Cu) to compare to similar calculations [16], in which the Peterson's VCC have been used, and with calculations [15] carried out by the atomic SCF program [4] as well. 相似文献
2.
Theilacker K Arbuznikov AV Bahmann H Kaupp M 《The journal of physical chemistry. A》2011,115(32):8990-8996
Due to their position-dependent exact exchange admixture, local hybrid functionals offer a higher flexibility and thus the potential for more universal and accurate exchange correlation functionals compared to global hybrids with a constant admixture, as has been demonstrated in previous work. Yet, the local hybrid constructions used so far do not account for the inclusion of dispersion-type interactions. As a first exploratory step toward a more general approach that includes van der Waals-type interactions with local hybrids, the present work has added DFT-D3-type corrections to a number of simple local hybrid functionals. Optimization of only the s(8) and s(r,6) parameters for the S22 set provides good results for weak interaction energies but deteriorates the excellent performance of the local hybrids for G3 atomization energies and for classical reaction barriers. A combined optimization of the two DFT-D3 parameters with one of the two parameters of the spin-polarized local mixing function (LMF) of a local hybrid for a more general optimization set provides simultaneously accurate dispersion energies, improved atomization energies, and accurate reaction barriers, as well as excellent alkane protobranching ratios. For other LMFs, the improvements of such a combined optimization for the S22 energies have been less satisfactory. The most notable advantage of the dispersion-corrected local hybrids over, for example, a B3LYP-D3 approach, is in the much more accurate reaction barriers. 相似文献
3.
4.
Hrobárik P Reviakine R Arbuznikov AV Malkina OL Malkin VG Köhler FH Kaupp M 《The Journal of chemical physics》2007,126(2):024107
The calculation of nuclear shieldings for paramagnetic molecules has been implemented in the ReSpect program, which allows the use of modern density functional methods with accurate treatments of spin-orbit effects for all relevant terms up to order Omicron(alpha4) in the fine structure constant. Compared to previous implementations, the methodology has been extended to compounds of arbitrary spin multiplicity. Effects of zero-field splittings in high-spin systems are approximately accounted for. Validation of the new implementation is carried out for the 13C and 1H NMR signal shifts of the 3d metallocenes 4VCp2, 3CrCp2, 2MnCp2, 6MnCp2, 2CoCp2, and 3NiCp2. Zero-field splitting effects on isotropic shifts tend to be small or negligible. Agreement with experimental isotropic shifts is already good with the BP86 gradient-corrected functional and is further improved by admixture of Hartree-Fock exchange in hybrid functionals. Decomposition of the shieldings confirms the dominant importance of the Fermi-contact shifts, but contributions from spin-orbit dependent terms are frequently also non-negligible. Agreement with 13C NMR shift tensors from solid-state experiments is of similar quality as for isotropic shifts. 相似文献
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6.
R Nirmala V Sankaranarayanan K Sethupathi AV Morozkin T Geethakumary Y Hariharan 《Pramana》2002,58(5-6):1101-1104
New R
2Ti3Ge4 (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac
magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize
in the parent, Sm5Ge4-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series.
The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales
with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays
a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects. 相似文献
7.
Following the suggestion of local hybrid functionals with position-dependent exact-exchange admixture [J. Jaramillo, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 1068 (2003)], a functional that mixes only local and exact exchange plus local correlation has been constructed. With a simple local mixing function for the position dependence, this Lh-SVWN functional provides atomization energies for the G2-1 set that are competitive with currently available state-of-the-art functionals like, e.g., B3LYP. This is achieved without generalized gradient approximations for exchange or correlation. 相似文献
8.
G. M. Zhidomirov A. V. Arbuznikov I. V. Yudanov N. A. Kachurovskaya 《Reaction Kinetics and Catalysis Letters》1996,57(2):263-274
A short review on the quantum chemical study of the Bronsted and Lewis acid sites (BAS and LAS) is presented. Various factors that strongly influence the power of BAS in zeolites are considered. Different possible ways of LAS formation in zeolites are dicussed. The probable mechanism of selective oxidation in FeHZSM-5 is considered and the resulting active site structure is calculatedab initio. The initial step of hydrogen peroxide activation in Ti-silicalite is studied and the scale of the energy of structural deformation to proceed during the reaction is evaluated. 相似文献
9.
Kaupp M Reviakine R Malkina OL Arbuznikov A Schimmelpfennig B Malkin VG 《Journal of computational chemistry》2002,23(8):794-803
We report the first implementation of the calculation of electronic g-tensors by density functional methods with hybrid functionals. Spin-orbit coupling is treated by the atomic meanfield approximation. g-Tensors for a set of small main group radicals and for a series of ten 3d and two 4d transition metal complexes have been compared using the local density approximation (VWN functional), the generalized gradient approximation (BP86 functional), as well as B3-type (B3PW91) and BH-type (BHPW91) hybrid functionals. For main group radicals, the effect of exact-exchange mixing is small. In contrast, significant differences between the various functionals arise for transition metal complexes. As has been shown previously, local and in particular gradient-corrected functionals tend to underestimate the "paramagnetic" contributions to the g-tensors in these cases and thereby recover only about 40-50% of the range of experimental g-tensor components. This is improved to ca. 60% by the B3PW91 functional, which also gives slightly reduced standard deviations. The range increases to almost 100% using the half-and-half functional BHPW91. However, the quality of the correlation with experimental data worsens due to a significant overestimate of some intermediate g-tensor values. The worse performance of the BHPW91 functional in these cases is accompanied by spin contamination. Although none of the functionals tested thus appears to be ideal for the treatment of electronic g-tensors in transition metal complexes, the B3PW91 hybrid functional exhibited the overall most satisfactory performance. Apart from the validation of hybrid functionals, some aspects in the treatment of spin-orbit contributions to the g-tensor are discussed. 相似文献
10.
Dr. Sandra Schinzel Johannes Schraut Dr. Alexei V. Arbuznikov Prof. Dr. Per E. M. Siegbahn Prof. Dr. Martin Kaupp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(34):10424-10438
Metal and ligand hyperfine couplings of a previously suggested, energetically feasible Mn4Ca model cluster ( SG2009?1 ) for the S2 state of the oxygen‐evolving complex (OEC) of photosystem II (PSII) have been studied by broken‐symmetry density functional methods and compared with other suggested structural and spectroscopic models. This was carried out explicitly for different spin‐coupling patterns of the S=1/2 ground state of the MnIII(MnIV)3 cluster. By applying spin‐projection techniques and a scaling of the manganese hyperfine couplings, computation of the hyperfine and nuclear quadrupole coupling parameters allows a direct evaluation of the proposed models in comparison with data obtained from the simulation of EPR, ENDOR, and ESEEM spectra. The computation of 55Mn hyperfine couplings (HFCs) for SG2009?1 gives excellent agreement with experiment. However, at the current level of spin projection, the 55Mn HFCs do not appear sufficiently accurate to distinguish between different structural models. Yet, of all the models studied, SG2009?1 is the only one with the MnIII site at the MnC center, which is coordinated by histidine (D1‐His332). The computed histidine 14N HFC anisotropy for SG2009?1 gives much better agreement with ESEEM data than the other models, in which MnC is an MnIV site, thus supporting the validity of the model. The 13C HFCs of various carboxylates have been compared with 13C ENDOR data for PSII preparations with 13C‐labelled alanine. 相似文献