Energy-consistent relativistic pseudopotentials for 3d-transition metals Sc to Ni based on modified valence energies are proposed. The pseudopotentials are adjusted at the finite
difference level within the intermediate coupling scheme with respect to multi-configuration Dirac–Hartree–Fock data based
on the Dirac–Coulomb Hamiltonian with an estimate of the Breit contributions in quasidegenerate perturbation theory. Typically
a few hundred to thousand J levels arising from about 35 to 40 configurations ranging from the anion down to the highly charged
cation are considered as references. It is shown that introducing a small common energetic shift of all valence energies reduces
the errors in the parameter adjustment considerably. Results of highly correlated atomic and molecular test calculations using
large basis sets and basis set extrapolation techniques are presented.
To be submitted to Theoretical Chemistry Accounts (special volume on the occasion of Prof. Dr. H. Stoll's 60th birthday) 相似文献
The diphosphate ester (ThDP) of thiamin (vitamin B1) is an important cofactor of enzymes within the carbohydrate metabolism. The initial reaction step shared by all ThDP-dependent enzymes is the deprotonation of the C2–H of the thiazolium ring. The replacement of the 4′-amino group by a hydroxyl one in the pyrimidine ring leads to the oxy-ThDP analogue which is known as an antagonist in thiamin catalysis.
Ab initio and DFT calculations on the MP2/6-31G* and B3LYP/6-31G* level were performed to study the proton relay function in thiamin and oxythiamin systems. Both MP2 and B3LYP calculations show significant differences of the reaction coordinate of the ylide formation in the systems. Tautomers, protonated and deprotonated species of both systems show different trends regarding their stability. The influence of correlation effects on the results is discussed by comparison with the HF-SCF/6-31G* data. Frequency calculations on the B3LYP/6-31G* level were performed to characterize the minima and transition state structures, respectively. 相似文献
Hydrogen abstraction reaction, H C2H4 --H2 C2H2 was studied by using A initio SCF method. Ge-ometries were fully optimized at SCF level and energies were computed at STO-3G basis set for reactants and transition state. Vibrational analysis was performed thereupon. Finally, the rate constant calculations were carried out at different temperatures for all range of reaction temperature according to Eyring's sbwlute reaction rate theory. The calculated activation energy is 12. 68 kcal/mol, lower than observed value (H. S kcal/mol) by 1. 82 kcal/mol only. The agreement of the calculated rate constants with the experiments is satisfactory. 相似文献
Contributions to the Chemistry of Transition Metal Alkyl Compounds. 58 On 2-(Dimethylaminomethyl)ferrocenyl Compounds of Vanadium, Molybdenum, Tungsten, Thorium, and Uranium Earlier results according to which dimethylaminomethylferrocenyl groups (FcN) are able to form stable organometallic chelate compounds were confirmed by synthesis of the heterobimetallic chelate compounds (FcN)2VO · Li(acac) II , (FcN)MoO2(acac) III , (FcN)WOCl3 IV , (FcN)Th(acac)3 V , and (FcN)UO2(acac) VI from the corresponding metal acetylacetonates or oxidchlorides and (FcN)Li I . The new compounds were characterized by elemental analysis, the i.r., 1H-n.m.r., and electron spectra and by their effective magnetic moments. 相似文献
Summary. DFT calculations were carried out on Ti2(OCH3)8 (NH2CH3)2 and Ti2(OCH3)8(NH3)2, which are model compounds for the previously isolated amine adducts Ti2(OR)8(NH2R′)2. The calculations show that the Ti–N bond strength is weak; however, coordination of the amine to the metal center is supported
by a N–H···O hydrogen bond of the amine with the neighboring alkoxo ligand. The Ti–N interaction is purely σ in nature, while
the Ti–O interactions include both σ and π contributions. The lowest unoccupied molecular orbitals are mainly localized on
Ti t2g-like orbitals. 相似文献
An overview is given on recent advances of density functional theory (DFT) as applied to the calculation of nuclear magnetic
resonance (NMR) chemical shifts and electron spin resonance (ESR) g-tensors. This is a new research area that has seen tremendous progress and success recently; we try to present some of these
developments. DFT accounts for correlation effects efficiently. Therefore, it is the only first-principle method that can
handle NMR calculations on large systems like transition-metal complexes. Relativistic effects become important for heavier
element compounds; here we show how they can be accounted for. The ESR g-tensor is related conceptually to the NMR shielding, and results of g-tensor calculations are presented. DFT has been very successful in its application to magnetic properties, for metal complexes
in particular. However, there are still certain shortcomings and limitations, e.g., in the exchange-correlation functional,
that are discussed as well.
Received: 24 October 1997 / Accepted: 19 December 1997 相似文献
The rational function optimization algorithm is one of the widely used methods to search stationary points on surfaces. However,
one of the drawbacks of this method is the step reduction procedure to deal with the overstepping problem. We present and
comment on a method such that the step obtained from the solution of the rational function equations possesses the desired
correct length. The analysis and discussion of the method is mainly centered on the location and optimization of transition
states.
Received: 18 June 1998 / Accepted: 17 September 1998 / Published online: 23 November 1998 相似文献
This paper describes the application of Snyman's dynamic minimisation method to a fitted potential surface of H3. Comparisons are made with conventional algorithms. A method is described to extend Snyman's method so that it will find only a particular kind of stationary point. It is emphasized that this method enables saddle points to be found without having to resort to approaches based on trial and error. 相似文献