Simplified SCF Method for σ-Bonded Systems. I. Physical Properties of Hydrogen Halides

Abstract

Approximate SCF LCAO—MO calculations have been carried out for the ground‐state properties of four hydrogen halides; six internuclear distances were considered. In the model only the bonding electrons are considered explicitly. The effect of the inner electrons were taken account of by semiempirical methods. The electron pair is described by a single configurational wavefunction and the MO's are built from 1s and np AO's. The matrix elements are obtained utilizing the Mayer—Sklar, Mulliken, Pariser, and Pople approximations. As a secondary study the effect of the Wolfsberg—Helmholtz parameter K, in the resonance terms is studied. The calculated binding energies, equilibrium bond distances, dipole moments, vibrational force constants, and breaking forces obey the same trends as in experimental data. Moreover the magnitudes for these calculated quantities are in substantial agreement with experiment. This agreement can be improved for a given physical property of the series by introducing the arbitrary parameter K and optimizing it for one member of the series. It is concluded that the approximations characterizing the model, all of which had been previously used with π‐bonded systems, are equally well applicable to σ‐bonded systems.