On the Approximate Relation Between the Sum of Semiempirical Molecular Orbital Energies and the Total Energy of a Molecule

1983 ◽  
Vol 38 (3) ◽  
pp. 313-316
Author(s):  
Zvonimir B. Maksić ◽  
Krešimir Rupnik
Keyword(s):  
Total Energy ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Electrostatic Potential ◽  
Original Form ◽  
Expectation Values ◽  
Approximate Relation ◽  
Type Formula ◽  
Orbital Energies ◽  
Energy Expectation

Abstract The Ruedenberg type formula relating the total molecular energy to the sum of orbital energies is examined by using SCC-MO and ab initio DZ MO eigenvalues. Comparison with rigorous ab initio DZ energy expectation values indicates that Ruedenberg’s formula in its original form can not provide semiquantitative information on molecular energetics. Much more promissing in this respect is the electrostatic potential at the nuclei approach of Politzer and Parr.

Non-empirical molecular orbital calculations based on Slater-type orbitals. A restricted use of Gaussian expansions

1973 ◽  
Vol 26 (6) ◽  
pp. 1151 ◽  
Author(s):  
RD Brown ◽  
FR Burden ◽  
GR Williams
Keyword(s):  
Total Energy ◽  
Ab Initio ◽  
Small Molecules ◽  
Molecular Orbital ◽  
Slater Type Orbitals ◽  
Molecular Orbital Calculations ◽  
Slater Type ◽  
Numerical Accuracy ◽  
Computational Speed ◽  
Restricted Use

An ab-initio SCFMO technique of balanced computational speed and precision is described for use with Slater-type orbitals as basis. All of the more significant integrals over STO'S are evaluated with full arithmetic accuracy but the ?non-NDDO? two-electron integrals are evaluated less precisely by using small Gaussian expansions. ��� The overall numerical accuracy achieved in calculations of total energy and <r> are illustrated for a number of small molecules using both 2G and 3G expansions. The performance, especially with respect to energy calculations, is clearly superior to that of analogous methods that have recently been described.

A Model Theoretical Study for Alkylation in Benzimidazoles: ab initio Electrostatic Potentials

1979 ◽  
Vol 32 (1) ◽  
pp. 11 ◽  
Author(s):  
AL Hinde ◽  
L Radom ◽  
M Rasmussen
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Electrostatic Potential ◽  
Molecular Electrostatic Potential ◽  
Theoretical Study ◽  
Molecular Orbital Theory ◽  
Frontier Orbital ◽  
Orbital Theory ◽  
Controlled Processes

Ab initio molecular orbital theory is used to study the protonation of benzimidazole anions. Both kinetically and thermodynamically controlled processes are considered for the unsubstituted and for NH2, NO2 and CN substituted systems. Extensive use is made of molecular electrostatic potential (m.e.p.) maps to predict kinetically preferred sites of protonation. Predictions made on this basis are consistent with experimental data on alkylation of these and closely related systems. In contrast, other approaches based on theoretical charges or frontier orbital coefficients do not correlate well with the experimental results.

A pairwise additivity scheme for conformational energies of substituted ethanes

1975 ◽  
Vol 343 (1632) ◽  
pp. 1-10 ◽  
Keyword(s):  
Large Deviations ◽  
Ab Initio ◽  
Dihedral Angle ◽  
Molecular Orbital ◽  
Methyl Groups ◽  
Molecular Orbital Calculations ◽  
Linear Combinations ◽  
Strongly Interacting ◽  
Conformational Energies

Ab initio molecular orbital calculations are used to explore additivity in the conformational energies of poly-substituted ethanes in terms of conformational energies of ethane and appropriate mono- and 1,2-di-substituted derivatives. Such relations would allow complex calculations for poly-substituted ethanes to be replaced by much simpler ones on a small number of parent molecules. General expressions for the linear combinations are derived from the assumption that interactions between vicinal substituents are pairwise additive and depend only on the vicinal dihedral angle. The additivity scheme is tested for 15 ethanes, di-, tri- or tetrasubstituted by cyano and methyl groups and for a smaller number of fluoroethanes. Additivity applies to within 0.1- 0.3 k J mol -1 in the methylethanes and mostly to within about 0.7- 0.8 kJ mol -1 in cyanoethanes. Large deviations are found among the geminally substituted fluoroethanes. It is suggested that the additivity approximation is most successful in the absence of strongly interacting geminal groups. Predictions are made of conformational energies of ten hexa(cyano- and methyl-) substituted ethanes.

Effect of Chromium and Vanadium on Nanolayered Ternary Carbides: AB Initio Study

2009 ◽  
Vol 609 ◽  
pp. 239-242
Author(s):  
A.E. Merad ◽  
M.B. Kanoun
Keyword(s):  
Electronic Structure ◽  
Total Energy ◽  
Ab Initio ◽  
Structural Parameters ◽  
Ab Initio Study ◽  
Generalized Gradient ◽  
Generalized Gradient Approximation ◽  
Full Relaxation ◽  
Relaxation Procedure ◽  
Ternary Carbides

The Cr2AlC and V2AlC nanolayered ternary carbides are studied by performing APW-lo ab initio total energy calculations within the recent Wu-Cohen generalized gradient approximation GGA. Using full relaxation procedure of the volume and the atomic positions we obtained the structural parameters and electronic structure of the optimization hexagonal. Results were compared with the experimental ones. Interesting features are deduced. In fact, we have shown why these materials are conductors.

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