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

Experimental Gas Phase 1H NMR Spectra and Basis Set Dependence of ab initio GIAOMO Calculations of 1H and 13C NMR Absolute Shieldings and Chemical Shifts of Small Hydrocarbons

2004 ◽  
Vol 59 (10) ◽  
pp. 1153-1176 ◽  
Author(s):  
Thomas Zuschneid ◽  
Holger Fischer ◽  
Thomas Handel ◽  
Klaus Albert ◽  
Günter Häfelinger
Keyword(s):  
Ab Initio ◽  
Gas Phase ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Basis Set ◽  
Basis Sets ◽  
Gaussian Basis Sets ◽  
Phase Measurements ◽  
H Nmr ◽  
Set Up

AbstractHigh-resolution gas phase measurements of 1H NMR spectra at 400 MHz and atmospheric pressure of seven small hydrocarbons are presented. The developed new method and the experimental set-up are described. Ab initio GIAO MO calculations of 1H and 13C NMR absolute shieldings on the HF, MP2 and B3LYP levels using 25 standard gaussian basis sets are reported for these hydrocarbons, based on experimental re distances. The measured gas phase 1H chemical shifts have been converted to an absolute σ0 shielding scale by use of the literature shielding of methane. These and gas phase 13C literature values have been transferred with literature ZPV data to estimated σeexp shieldings which are used to evaluate the basis set dependence of the calculated σe shieldings utilizing linear least squares regressions. Exponential extrapolations of Dunning basis set calculations allow the determination of basis set limits for 1H and 13C shieldings. 1H and 13C chemical shifts have been derived from the HF calculated shieldings with shieldings of TMS which has been geometry optimized and GIAO calculated in each basis. Standard deviations (esd) as low as 0.09 ppm for 1H and 0.76 ppm for 13C calculations have been obtained.The statistically best basis set for simultaneous calculation of 1H and 13C absolute shieldings or relative shifts is 6-311G* within the HF and B3LYP methods. Aiming for highest accuracy and precision, 1H and 13C have to be treated separately. In this case, best results are obtained using MP2/6-311G** or higher for 1H shieldings and MP2/cc-pVTZ for 13C shieldings.

The simplified ab initio method calculation of linear polarizability

1973 ◽  
Vol 26 (5) ◽  
pp. 921 ◽  
Author(s):  
RD Brown ◽  
GR Williams
Keyword(s):  
Ab Initio ◽  
Small Molecules ◽  
Basis Set ◽  
Basis Sets ◽  
Orbital Method ◽  
Polarizability Anisotropy ◽  
Minimal Basis ◽  
Hartree Fock ◽  
Numerical Performance ◽  
Experimental Values

The simplified ab-initio molecular-orbital method described previously is particularly suited to the calculation of polarizabilities by the non-perturbative coupled Hartree-Fock technique. Trial calculations on CO and HF, for which comparison with corresponding ab-initio calculations is possible, show that the method gives an adequate numerical performance. Minimal basis set calculations in general tend to give values that are considerably too low because of inadequate flexibility of the basis and this is the origin of the large discrepancy between theory and experiment, especially for small molecules. ��� Results are also reported for N2O and O3. For these larger systems the SAI results with minimal basis sets are noticeably nearer experimental values. The polarizability anisotropy for N2O is particularly well reproduced by the SAI method. �

Small Gaussian basis sets for molecular calculations. II. Effect of basis set size on the calculated wavefunction and a useful GTO basis set

1973 ◽  
Vol 26 (7) ◽  
pp. 1381 ◽  
Author(s):  
FR Burden ◽  
BT Hart
Keyword(s):  
Wave Functions ◽  
Basis Set ◽  
Basis Sets ◽  
Confidence Limits ◽  
Optimum Size ◽  
Minimal Basis ◽  
Gaussian Basis Sets ◽  
Large Molecules ◽  
Set Size ◽  
Molecular Calculations

A quantitative assessment of the importance of basis set variation at the minimal basis level of accuracy has been carried out. A number of basis sets, using Gaussian lobe functions, were tested by calculating the energy and one-electron properties for a number of molecules and the results used to select an optimum sized accurate basis set. This basis set consisted of a five-component 1s-Gaussian type orbital (GTO), a three-component 2s-GTO and a three-component 2p-GTO for each first row atom, and a three-component 1s-GTO for hydrogen. The accuracy of wave functions calculated with the minimal basis sets was very sensitive to changes in the 2p-GTO. ��� A Gaussian lobe basis set of optimum size for use with large molecules is given. The results of testing this set by calculating several one-electron properties for ten molecules, together with confidence limits, are also presented.

Nonempirical s.c.f. calculations on sulfur atom, hydrogen sulfide, and dihydrogen sulfoxide

1968 ◽  
Vol 46 (8) ◽  
pp. 1205-1214 ◽  
Author(s):  
A. Rauk ◽  
I. G. Csizmadia
Keyword(s):  
Multiple Bond ◽  
Optimization Procedure ◽  
Basis Set ◽  
Basis Sets ◽  
Minimal Basis ◽  
Gaussian Basis Sets ◽  
Chemical Systems ◽  
A Value ◽  
Self Consistent Field ◽  
Sulfur Containing

This paper reports the first attempt to use Gaussian basis sets in nonempirical self-consistent field (s.c.f.) calculations on sulfur-containing chemical systems. Exponents for Gaussian-type functions (G.t.f.) on S atom are given for the minimal basis set. The optimization procedure is described and the optimized exponents utilized on calculations on S atom, H2S, and the hypothetical dihydrogen sulfoxide (H2SO). Calculations by the minimal basis set of (G.t.f.), using these exponents, gave a value for the HSH angle of H2S that agrees well with the experimentally determined value. Calculations of H2SO support a "multiple bond" picture of the S—O bond.

Systematic sequences of well-balanced Gaussian basis sets

1994 ◽  
Vol 72 (7) ◽  
pp. 1741-1752 ◽  
Author(s):  
Mariusz Klobukowski
Keyword(s):  
Molecular Structure ◽  
Ab Initio ◽  
Basis Set ◽  
Basis Sets ◽  
Structure And Properties ◽  
Gaussian Basis Sets ◽  
Molecular Calculations

Systematic sequences of Gaussian basis sets with controlled energy errors for the studies of convergence of the basis set effects on the computed results of molecular calculations are presented. The basis sets were prepared for atoms H–Ne and Al–Ar and may be used in systematic ab initio ad limitem studies of molecular structure and properties.

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

Net charges and valence AO's in the methylamines; the hydrogen basis set and the properties of nitrogen

1985 ◽  
Vol 63 (7) ◽  
pp. 1487-1491 ◽  
Author(s):  
Giuseppe Del Re ◽  
Sándor Fliszár ◽  
Michel Comeau ◽  
Claude Mijoule
Keyword(s):  
Basis Set ◽  
Basis Sets ◽  
Methyl Groups ◽  
Extended Form ◽  
Amine Nitrogen ◽  
Methyl Group ◽  
Net Charges ◽  
Extended Basis

Net charges and valence AO's for ammonia, methylamine, dimethylamine, and trimethylamine were calculated using extended basis sets. Superposition effects, evaluated by replacing Pople's standard 6-31G* basis by an extended form in which the basis of the ammonia H atoms and of the methyl groups of trimethylamine are retained in the treatment of each molecule, indicate that the quality of the treatment of amine nitrogen atoms is strongly dependent on the number of methyl groups. A new, augmented basis is proposed for the hydrogens, which appears to be reasonably well balanced: comparison with familiar (e.g., 6-31G*) calculations illustrates in what manner the treatment of nitrogen is worsened when even just one methyl group is replaced by hydrogen unless the impoverishment of the basis is suitably taken care of.

scholarly journals Stable Occupancy of Hydrogen Molecules in Clathrate Hydrates and + THF Clathrate Hydrates Determined by Ab Initio Calculations

2010 ◽  
Vol 2010 ◽  
pp. 1-6 ◽  
Author(s):  
Prasad Yedlapalli ◽  
Sangyong Lee ◽  
Jae W. Lee
Keyword(s):  
Ab Initio ◽  
Binding Energies ◽  
Clathrate Hydrates ◽  
Basis Set ◽  
Large Cavity ◽  
Basis Sets ◽  
Pure Hydrogen ◽  
Point Energy ◽  
Small Cavity ◽  
Hydrogen Molecules

Structure II clathrate hydrates of pure hydrogen and binary hydrates of are studied using ab initio calculations to determine the stable occupancies of small cavities. Ab initio calculations are carried out for a double cavity consisting of one dodecahedron (small cavity) and one hexakaidecahedron (large cavity). These two cavities are attached to each other as in sII hydrates to form a double cavity. One or two molecules are placed in the small cavity and one THF (or 4 molecules) molecule is placed in the large cavity. We have determined the binding energies of the double cavities at the MP2 level using various basis sets (3-21G, 3-21G(2p), 3-21 G(2p), 6-31G, 6-31G(2p), and 6-31 G(2p)). Different basis sets yield different stable occupancies of the small cavity. The results from the highest basis set (6-31 G(2p) with zero point energy corrections) indicate that the single occupancy is slightly more favorable than the double occupancy in both the cases of pure hydrates and THF + double hydrates.

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