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91.
Even systems in which strong electron correlation effects are present, such as the large near-degeneracy correlation in a
dissociating electron pair bond exemplified by stretched H2, are represented in the Kohn–Sham (KS) model of non-interacting electrons by a determinantal wavefunction built from the
KS molecular orbitals. As a contribution to the discussion on the status and meaning of the KS orbitals we investigate, for
the prototype system of H2 at large bond distance, and also for a one-dimensional molecular model, how the electron correlation effects show up in the
shape of the KS σ
g
orbital. KS orbitals φHL and φFCI obtained from the correlated Heitler-London and full configuration interaction wavefunctions are compared to the orbital
φLCAO, the traditional linear combination of atomic orbitals (LCAO) form of the (approximate) Hartree-Fock orbital. Electron correlation
manifests itself in an essentially non-LCAO structure of the KS orbitals φHL and φFCI around the bond midpoint, which shows up particularly clearly in the Laplacian of the KS orbital. There are corresponding
features in the kinetic energy density t
s
of the KS system (a well around the bond midpoint) and in the one-electron KS potential v
s
(a peak). The KS features are lacking in the Hartree-Fock orbital, in a minimal LCAO approximation as well as in the exact
one.
Received: 11 December 1996 / Accepted: 10 January 1997 相似文献
92.
Qing Z Wen-Chen Z Xiao-Xuan W Yang M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(4-5):769-772
From the high-order perturbation formulas of EPR parameters (zero-field splitting D, g factors gparallel, gperpendicular and hyperfine structure constants Aparallel, Aperpendicular) based on the two spin-orbit coupling parameter model for 3d3 ions in trigonal symmetry, the EPR parameters of Cr3+ and V2+ ions in HfS2 crystals are calculated. From the calculations, it is found that the local trigonal distortion angle theta of impurity center in HfS2:Cr3+ is smaller than that in HfS2:V2+. The dominant cause of the small zero-field splitting |D| and g-anisotropy |Deltag|=|gparallel-gperpendicular| in HfS2:Cr3+ (compound to HfS2:V2+) is due to the small local trigonal distortion angle theta rather than to the small impurity-ligand distance R in HfS2:Cr3+. 相似文献
93.
Hermann Stoll Gerhard Wagenblast Heinzwerner Preuβ 《Theoretical chemistry accounts》1980,57(2):169-178
Two procedures are discussed for the direct variational optimization of localized molecular orbitals which are expanded in local subsets of the molecular basis set. It is shown that a Newton-Raphson approach is more efficient than an iterative diagonalization scheme. The effect of the basis-set truncation on the quality ofab-initio SCF results is investigated for Be, Li2, HF, H2O, NH3, CH4 and C2H6. 相似文献
94.
95.
The structure of the local anaesthetic benzocaine was solved by direct methods and refined to anR of 0·12 for 531 observed reflections. The packing of the molecule is stabilised by N−H … O hydrogen-bonds (2–97 ?). The alkyl
chain attached to the benzene ring is intrans-trans conformation. The benzoic moiety shows a quinonoid character as found in some other local anaesthetics.
DCB contribution No. 699 相似文献
96.
In the research on metallic glass, there are arguments against the "rigid band charge transfer", model which assumes a charge transfer from metalloid atoms to transition metal atoms to explain the experimental evidence of linear reduction of average atomic magnetic moment with the increasing concentration of metalloid atoms, but they could not explain the experimental relation of the reduction. In the present work, spin-polarized SCC-DV-X_a calculation for atomic clusters for metallic glass Co-B has been empoloyed to investigate the local electronic structure and magnetic property of the metallic glass. As opposed to the "rigid band charge transfer" model, calculation in the present work indicates that charge transfers from Co4s to both B and Co3d. It is found that there is Co3d4s-B2p hybird bonding in Co-B, which leads to the linear reduction of average atomic magnetic moment. Thus the explanation removes the above controversy. 相似文献
97.
98.
99.
Sergei N. Yurchenko Jürgen Breidung Walter Thiel 《Theoretical chemistry accounts》2005,114(4-5):333-340
We report a theoretical study of the ground electronic state of BiH3. The potential energy surface (PES) is obtained from coupled cluster CCSD(T) calculations with a large basis set (289 contracted
Gaussian functions). The previously available quartic force field (P4) is extended by adding the dominant quintic and sextic
stretching terms to yield improved potential functions in symmetry coordinates (P6) and Morse-type coordinates (M4). Second-order
rovibrational perturbation calculations on the P4-PES and full variational calculations on the P6-PES and M4-PES yield almost
identical vibrational term values which is rationalized by considering the local mode behavior of BiH3 and the Morse-type character of the M4-PES. The remaining deviations between the computed and observed vibrational term values
must thus be caused by imperfections in the CCSD(T) surface. A refinement of this ab initio surface by a restrained fit to
experimental data allows an essentially perfect reproduction of the observed vibrational term values. Variational calculations
on this refined surface provide predictions for several overtone and combination bands that have not yet been observed.
Dedicated to Hermann Stoll on the occasion of his 60th birthday 相似文献
100.
The vapor pressures and osmotic coefficients of solutions of (R4N)2[MoS4] (R = ethyl, n-propyl and n-butyl) in acetone have been measured by head space-gas chromatography (HS-GC). Experimental data for the osmotic coefficients have been expressed by three thermodynamic models including the ionic interaction model of Pitzer, the electrolyte non-random two liquid (e-NRTL) model and the non-random factor (NRF) model. The ability of the models to fit the osmotic coefficient was compared on the basis of the standard deviation of the fittings. The results show that the considered models provide reliable results, but the Pitzer's model gives better results than the NRTL and the NRF methods, especially in the dilute region. 相似文献