Molecular calculations with the MODPOT, VRDDO, and MODPOT/VRDDO procedures: I. HF, F2, HCl, Cl2, formamide, pyrrole, pyridine, and nitrobenzene

Abstract

The nonempirical valence electron LCAO-MO-SCF model potential (MODPOT) procedure of Bonifacic and Huzinaga has been applied to the HF, F2, HCl, Cl2, formamide, pyrrole, pyridine, and nitrobenzene molecules. The results indicate that the method gives quite accurate valence orbital energies and potential energy curves for diatomics composed of first- and second-row atoms. It gives quite reliable valence orbital energies, gross atomic populations, total overlap populations, and dipole moment for moderately large organic molecules composed of first-row atoms and hydrogen. Use of the MODPOT approximation results in a substantial reduction in computer time and number of two-electron integrals that have to be processed. The nonempirical LCAO-MO-SCF charge-conserving variable retention of diatomic differential overlap (VRDDO) approximation of Wilhite and Euwema has been applied to the pyrrole, pyridine, and nitrobenzene molecules. The results indicate that the procedure gives accurate orbital energies, total energy, gross atomic populations, total overlap populations, and dipole moment for moderately large organic molecules. Use of the VRDDO approximation results in a substantial reduction in computer time. We also present pyrrole, pyridine, and nitrobenzene results obtained by introducing the VRDDO approximation into the MODPOT procedure. The accuracy of the VRDDO method remains unchanged if one considers only the valence electrons and there is an additional reduction in computer time.