Electronegativity Equalization and the Deformation of Atomic Orbitals in Molecular Wavefunctions

1988 ◽  
Vol 41 (6) ◽  
pp. 827 ◽  
Author(s):  
E Magnusson
Keyword(s):  
Hydrogen Atom ◽  
Bond Distance ◽  
Basis Sets ◽  
Radial Dependence ◽  
Electronic Charge ◽  
Atomic Orbitals ◽  
Electronegativity Equalization ◽  
Electronegativity Difference ◽  
The Mean ◽  
Molecular Wavefunctions

Electronegativity equalization, which must accompany the formation of a chemical bond, occurs when electronic charge is transferred between the bound atoms but also by changes in the radial dependence of the atomic orbitals involved in the bonding. The degree of contraction or expansion of the atomic orbitals may be studied by analysing ab initio MO wavefunctions calculated with flexible basis sets. The effects on the hydrogen orbital are marked, the 1sHmean radius being progressively reduced by 9-23% across the series of first row hydrides (BH3 to HF) from its value in the hydrogen atom. The mean radius of the carbon 2p function in the wavefunctions of substituted methanes (CH3BH2 to CH3F) is correspondingly reduced by 2-19% from its free-atom value. Orbital contraction (or expansion) is dependent on bond distance, on the electronegativity difference of the bound atoms, and, because it varies from one MO to another, on the nature of the MO'S. The effects are greatest in MO'S which are strongly bonding.

scholarly journals The positive ionisation produced by platinum and by certain salts when heated

1913 ◽  
Vol 88 (601) ◽  
pp. 117-146 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Hydrogen Atom ◽  
Royal Society ◽  
Platinum Electrode ◽  
Mean Value ◽  
Electronic Charge ◽  
Aluminium Phosphate ◽  
Positive Ions ◽  
A Value ◽  
The Mean

In the 'Proceedings of the Royal society' for 1910, there is an account of a spectroscopic investigation of the nature of the carriers of positive electricity when an electric current is sent from a glowing platinum strip covered with aluminium phosphate to a surrounding platinum electrode, the whole being contained in a highly evacuated vessel. It was found that aluminium phosphate heated under these conditions evolved carbon monoxide gas, and as a molecule of this gas earning a single electronic, charge gives a value for e/m which agrees fairly well with the mean value found for the carriers of positive electricity from beaded metals, it was concluded that the positive ions are charged molecules of carbon monoxide. Hydrogen was also detected in the gas evolved by the hot electrode in this experiment, and it now seems probable that atoms of hydrogen also take part in carrying the current, for Garrett has found that about 10 per cent, of the positive ions present when aluminium phosphate is beaded on a platinum strip in a vacuum have a mass corresponding to that of the hydrogen atom.

DFT Benchmark Study of the O--O Bond Dissociation Energy in Peroxides Validated with High-Level Ab-Initio Calculations

2019 ◽  
Author(s):  
Danilo Carmona ◽  
Pablo Jaque ◽  
Esteban Vöhringer-Martinez
Keyword(s):  
Reference Value ◽  
Basis Set ◽  
Basis Sets ◽  
Mean Deviation ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
The Mean ◽  
Experimental Values ◽  
High Level ◽  
Almost All

<div><div><div><p>Peroxides play a central role in many chemical and biological pro- cesses such as the Fenton reaction. The relevance of these compounds lies in the low stability of the O–O bond which upon dissociation results in radical species able to initiate various chemical or biological processes. In this work, a set of 64 DFT functional-basis set combinations has been validated in terms of their capability to describe bond dissociation energies (BDE) for the O–O bond in a database of 14 ROOH peroxides for which experimental values ofBDE are available. Moreover, the electronic contributions to the BDE were obtained for four of the peroxides and the anion H2O2− at the CBS limit at CCSD(T) level with Dunning’s basis sets up to triple–ζ quality provid- ing a reference value for the hydrogen peroxide anion as a model. Almost all the functionals considered here yielded mean absolute deviations around 5.0 kcal mol−1. The smallest values were observed for the ωB97 family and the Minnesota M11 functional with a marked basis set dependence. Despite the mean deviation, order relations among BDE experimental values of peroxides were also considered. The ωB97 family was able to reproduce the relations correctly whereas other functionals presented a marked dependence on the chemical nature of the R group. Interestingly, M11 functional did not show a very good agreement with the established order despite its good performance in the mean error. The obtained results support the use of similar validation strategies for proper prediction of BDE or other molecular properties by DF Tmethods in subsequent related studies.</p></div></div></div>

The structure and energetics of low-lying states of RCO and RNN free radicals

1977 ◽  
Vol 55 (5) ◽  
pp. 863-868 ◽  
Author(s):  
N. Colin Baird ◽  
Harish B. Kathpal
Keyword(s):  
Experimental Data ◽  
Free Radicals ◽  
Hydrogen Atom ◽  
Ab Initio ◽  
Open Shell ◽  
Basis Set ◽  
Basis Sets ◽  
Mo Calculations ◽  
Decomposition Products ◽  
Ab Initio Mo Calculations

The important geometrical variables in the structures of the lowest 2A′ and 2A′′ states of the free radicals HCO, CH3CO, NH2CO, HNN, and CH3NN have been determined by ab initio MO calculations using the STO-3G basis set. The energy differences between the states, and the energies of the radicals relative to their decomposition products and relative to their hydrogen atom addition products, are reported using both STO-3G and 4-31G basis sets in the restricted open-shell calculations. The trends in these results and their relation to available experimental data are discussed.

The crystal and molecular structure of thioformaldehyde trimer

1967 ◽  
Vol 45 (4) ◽  
pp. 353-357 ◽  
Author(s):  
J. E. Fleming ◽  
H. Lynton
Keyword(s):  
Crystal And Molecular Structure ◽  
Three Dimensional ◽  
Bond Distance ◽  
Orthorhombic Space Group ◽  
Significant Difference ◽  
The Mean ◽  
Temperature Factors ◽  
No Absorption ◽  
Good Agreement ◽  
Atomic Parameters

Crystals of thioformaldehyde trimer, (CH2S)3 are orthorhombic, space group Pmn21 with a = 7.697 Å [Formula: see text], b = 7.067 Å [Formula: see text], c = 5.323 Å [Formula: see text]. There are two molecules in the unit cell with sulfur and carbon atoms in positions (4b) and (2a). The atomic parameters for sulfur and carbon have been determined from a three-dimensional analysis using observed and calculated differential syntheses with isotropic temperature factors. No absorption corrections were applied to the intensity data and no attempt has been made to establish the hydrogen positions. The final discrepancy index is R = 0.093. The molecule has the chair configuration and shows no significant difference between the lengths of any S—C bonds. The mean S—C bond distance is 1.818 Å and the standard deviation of the mean is 0.003 Å. This value is in good agreement with the commonly accepted value of 1.817 ± 0.005 Å for the S—C paraffinic bond.

Improvement of the long-range behavior of Gaussian basis sets using asymptotic constraints

1992 ◽  
Vol 70 (2) ◽  
pp. 362-365 ◽  
Author(s):  
Toshikatsu Koga ◽  
Ajit J. Thakkar
Keyword(s):  
Long Range ◽  
Basis Sets ◽  
Gaussian Basis Sets ◽  
Atomic Orbitals ◽  
Hartree Fock

It is suggested that atomic orbitals with improved long-range behavior can be obtained by using energy-optimized Gaussian basis sets to which Gaussians have been added to satisfy a subset of some recently derived constraints that must be satisfied by the exact Hartree–Fock orbitals. This procedure is demonstrated by illustrative calculations for helium. This method is found to be superior to the adhoc method of adding diffuse Gaussians in an even-tempered fashion. Keywords: Gaussian basis sets, long-range behavior, asymptotic constraints.

The Effects of Split Valence Basis Sets on Muon Hyperfine Interaction in Guanine Nucleobase and Nucleotide Structures

2019 ◽  
Vol 966 ◽  
pp. 222-228 ◽  
Author(s):  
Wan Nurfadhilah Zaharim ◽  
Shukri Sulaiman ◽  
Siti Nuramira Abu Bakar ◽  
Nur Eliana Ismail ◽  
Harison Rozak ◽  
...  
Keyword(s):  
Total Energy ◽  
Hyperfine Interactions ◽  
Phosphate Group ◽  
Basis Set ◽  
Basis Sets ◽  
Cluster Method ◽  
Sugar Phosphate ◽  
Atomic Orbitals ◽  
Fermi Contact ◽  
Triple Zeta

The DFT cluster method was employed to investigate the electronic structures and muonium hyperfine interactions in guanine nucleobase and nucleotide using three different basis sets. The total energy and Fermi contact values were calculated for muon trapped at carbon '8'. The three basis sets, 6-31G, 6-311G and 6-311G(d,p), were used in tandem with the B3LYP functional. There are significant quantitative differences in the calculated total energy. 6-311G(d,p) produced the lowest total energy as compared to the other basis sets. The lowering of the total energy is due to the increase in the number of basis functions to describe the atomic orbitals, which is consistent with the postulate on basis set completeness. The 6-31G basis set produced the muon Fermi contact value that is the closest to the experimental value. The calculated Fermi contact values for the nucleobase and nucleotide are significantly lowered in going from the double-zeta to the triple-zeta basis set by 5% and 4% respectively. The lowering of the Fermi contact value can be attributed to the extension of the triple-zeta basis set in describing the valence atomic orbitals. The presence of the sugar phosphate group in the nucleotide instead of the methyl group tends to lower the Fermi contact value. Thus, the sugar phosphate group should be taken into consideration when designing a calculation model.

Static Dipole Polarizability of N-Octane Calculated With MinPol Basis Sets

2006 ◽  
Vol 2 (3) ◽  
pp. 139-147
Author(s):  
George Maroulis
Keyword(s):  
Systematic Study ◽  
Experimental Results ◽  
Basis Sets ◽  
Dipole Polarizability ◽  
Polarized Basis Sets ◽  
Yield Values ◽  
The Mean

We present a systematic study of the dipole polarizability of n-octane. Our investigation relies on the recently proposed minimally polarized basis sets (MinPOL). It is shown that these small basis sets yield values for the mean and the anisotropy of the polarizability convincingly close to the available experimental results.

Sign in / Sign up

Export Citation Format

Share Document