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 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

The Rotational Barrier About the Disulphide Bridge in Dimethyl Disulphide: An Ab Initio Study

1984 ◽  
Vol 39 (5) ◽  
pp. 495-498
Author(s):  
V. Renugopalakrishnan ◽  
R. Walter
Keyword(s):  
Ab Initio ◽  
Rotational Barrier ◽  
Basis Set ◽  
Basis Sets ◽  
Disulphide Bridge ◽  
Minimal Basis ◽  
Gaussian Basis Sets ◽  
Type Function ◽  
Dimethyl Disulphide ◽  
Extended Basis

An ab initio molecular orbital technique was used to investigate the rotational barrier about the disulphide bridge in dimethyl disulphide. Various minimal and extended basis sets were used in the calculations. The chosen minimal basis set was the STO-3G set, and the extended basis sets were the STO 4-31G set, the Dunning and Hay set consisting of contracted Gaussian basis sets: [2s], [3s, 2p] and [6s, 4p] for H, C, and S atoms, and the Dunning and Hay basis set augmented with a d-type function on S atoms. The total energy was calculated as a function of the torsion angle about the disulphide bond. The barrier to rotation about this bond was found to be two-fold in nature, in accordance with previous findings. The heights of the barriers were observed to depend upon the basis set and input geometry. For our particular choice of basis sets and input geometry, the calculated value of the eis and trans barriers ranged from 12.68 to 16.49 kcal/mol and from 6.23 to 8 kcal/mol, respectively. Inclusion of a d-type function in the basis sets was found to result in better agreement between the calculated and experimental values, thereby emphasizing the need for considering 3d orbitals of sulphur in MO calculations

Ab initio crystal orbital calculations on (CH)n and (HF)n with extended basis sets

1984 ◽  
Vol 26 (S18) ◽  
pp. 153-159 ◽  
Author(s):  
Y. J. I'haya ◽  
S. Narita ◽  
Y. Fujita ◽  
H. Ujino
Keyword(s):  
Ab Initio ◽  
Basis Sets ◽  
Crystal Orbital ◽  
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.

A Systematic DFT Study of Two Elementary Steps Involving Hydrogen Peroxide and the Hydroxyl Radical in the Fenton Reaction

2018 ◽  
Author(s):  
Danilo Carmona ◽  
David Contreras ◽  
Oscar A. Douglas-Gallardo ◽  
Stefan Vogt-Geisse ◽  
Pablo Jaque ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Hydroxyl Radical ◽  
Ab Initio ◽  
Fenton Reaction ◽  
Basis Set ◽  
Basis Sets ◽  
Dft Methods ◽  
Elementary Steps ◽  
Oxygen Oxygen ◽  
Complete Basis Set

The Fenton reaction plays a central role in many chemical and biological processes and has various applications as e.g. water remediation. The reaction consists of the iron-catalyzed homolytic cleavage of the oxygen-oxygen bond in the hydrogen peroxide molecule and the reduction of the hydroxyl radical. Here, we study these two elementary steps with high-level ab-initio calculations at the complete basis set limit and address the performance of different DFT methods following a specific classification based on the Jacob´s ladder in combination with various Pople's basis sets. Ab-initio calculations at the complete basis set limit are in agreement to experimental reference data and identified a significant contribution of the electron correlation energy to the bond dissociation energy (BDE) of the oxygen-oxygen bond in hydrogen peroxide and the electron affinity (EA) of the hydroxyl radical. The studied DFT methods were able to reproduce the ab-initio reference values, although no functional was particularly better for both reactions. The inclusion of HF exchange in the DFT functionals lead in most cases to larger deviations, which might be related to the poor description of the two reactions by the HF method. Considering the computational cost, DFT methods provide better BDE and EA values than HF and post--HF methods with an almost MP2 or CCSD level of accuracy. However, no systematic general prediction of the error based on the employed functional could be established and no systematic improvement with increasing the size in the Pople's basis set was found, although for BDE values certain systematic basis set dependence was observed. Moreover, the quality of the hydrogen peroxide, hydroxyl radical and hydroxyl anion structures obtained from these functionals was compared to experimental reference data. In general, bond lengths were well reproduced and the error in the angles were between one and two degrees with some systematic trend with the basis sets. From our results we conclude that DFT methods present a computationally less expensive alternative to describe the two elementary steps of the Fenton reaction. However, choice of approximated functionals and basis sets must be carefully done and the provided benchmark allows a systematic validation of the electronic structure method to be employed

Sign in / Sign up

Export Citation Format

Share Document