An ab initio investigation of disiloxane using extended basis sets and electron correlation

1992 ◽  
Vol 96 (20) ◽  
pp. 7958-7965 ◽  
Author(s):  
John B. Nicholas ◽  
Randall E. Winans ◽  
Robert J. Harrison ◽  
Lennox E. Iton ◽  
Larry A. Curtiss ◽  
...  
Keyword(s):  
Ab Initio ◽  
Electron Correlation ◽  
Basis Sets ◽  
Extended Basis

An ab initio Study of the Molecular Electric-field Gradients of the Chlorsilanes

1996 ◽  
Vol 51 (1-2) ◽  
pp. 41-45
Author(s):  
H. U. Suter ◽  
D. M. Maric ◽  
P. F. Meier
Keyword(s):  
Electric Field ◽  
Ab Initio ◽  
Electron Correlation ◽  
Basis Sets ◽  
Quadrupole Moments ◽  
Electric Field Gradients ◽  
Field Gradients ◽  
Extended Basis ◽  
Good Agreement ◽  
Nuclear Quadrupole Moments

Abstract The electric field gradient (EFG) of chlorine in the chlorine containing silanes (SiCl4 , SiCl3H, SiCl2H2 , and SiClH3) was determined by means of ab initio methods and compared to recent experiments from which nuclear quadrupole moments are extracted. A careful estimation of the AO basis sets and the effect of the electron correlation is undertaken. The results showed the importance of the use of extended basis sets in the calculation of EFGs in second row atoms. Good agreement with deviations less than 5% from the experiments was found. The effect of the electron correlation was found to be small.

CONFORMATIONAL AND DYNAMICAL PROPERTIES OF THE C(O)–CH2–S–H MOIETY IN THIOGLYCOLIC ACID AND METHYLTHIOGLYCOLATE: AN AB INITIO AND DFT STUDY

2002 ◽  
Vol 01 (02) ◽  
pp. 309-317
Author(s):  
A. C. FANTONI
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Electron Correlation ◽  
Thioglycolic Acid ◽  
Basis Sets ◽  
Geometrical Parameters ◽  
Molecular Orbital Calculations ◽  
Dynamical Properties ◽  
Extended Basis ◽  
Different Levels

The results of a series of ab initio molecular orbital calculations on thioglycolic acid and methylthioglycolate are presented. Full geometry optimizations at different levels of theory have been performed for the equilibrium and transition state configurations, in order to determine the height of the inversion barriers, and to obtain information on the relaxation of some geometrical parameters. In spite of using extended basis sets and the inclusion of electron correlation, there is an important inconsistency between the relative position of the thiolic hydrogen derived from experimental data and the ab initio predictions. As regards the barrier height, the results more consistent with the available experimental data are obtained when the Gaussian2 compound methods [G2 and G2(MP2)] are used. The possible influence of an –S–H⋯O = hydrogen bond on the conformational behavior has also been investigated by analyzing the topology of the electron density.

Ab initio MP2 study of the HF ... ClF complex using various extended basis sets and bond functions

1996 ◽  
Vol 93 (6) ◽  
pp. 333-342
Author(s):  
Josefredo R. Pliego ◽  
Stella M. Resende ◽  
Wagner B. Almeida
Keyword(s):  
Ab Initio ◽  
Basis Sets ◽  
Bond Functions ◽  
Extended Basis

Ab initio molecular orbital study of simple 1,3-dipolar reactions

1976 ◽  
Vol 29 (3) ◽  
pp. 465 ◽  
Author(s):  
D Poppinger
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Transition States ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Molecular Orbital Study ◽  
Orbital Study ◽  
Extended Basis ◽  
Optimized Geometries

Ab initio molecular orbital calculations with minimal and extended basis sets have been carried out for the 1,3-dipolar addition of fulminic acid to acetylene, ethylene, ethynamine and propynenitrile. Optimized geometries are reported for the transition states HCNO+C2H2, HCNO+C2H4, HCNO+ C2HNH2, for the adducts isoxazole and 2-isoxazoline, and for nitrosocyclopropene as a possible intermediate. The calculations indicate that (a) these 1,3-dipolar reactions are synchronous processes, (b) the geometry of the transition state is insensitive to substitution and (c) of the isomeric substituted adducts, 5-aminoisoxazole and isoxazole-4-carbonitrile should be formed preferentially.

An approximate ab initio method based on the DIM model

2000 ◽  
Vol 78 (12) ◽  
pp. 1575-1586 ◽  
Author(s):  
John M Cullen
Keyword(s):  
Ab Initio ◽  
Excited States ◽  
Electron Correlation ◽  
Correlation Energy ◽  
Basis Sets ◽  
Ab Initio Method ◽  
First Order ◽  
Hartree Fock ◽  
Modified Method ◽  
Electron Correlation Energy

Using a second quantized formulation, an approximate diatomics in molecules (DIM) theory is presented in which all three- and four-centered electronic integrals are neglected. To ameliorate the effects of this approximation, the DIM one electron operator is constructed so that the true ab initio first-order density matrix and total energy are reproduced at the Hartree–Fock level. The resulting model was extensively tested for a variety of basis sets for its capability of capturing both the dynamic and nondynamic components of the electron correlation energy as well as the energies of excited electronic states. A modified method in which the DIM one-electron operator is formed from the initial extended Hückel guess of the Hartree–Fock orbitals was also found to produce excellent results.Key words: DIM, electron correlation energy, excited states, semiempirical.

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