VALENCE-BOND STRUCTURE-FUNCTION AND BONDE D FUNCTION .1. THEORETICAL METHOD AND APPLICATION TO METHANE

The bonded tableau is expanded in a series of bonded functions of diff erent order, where the zero-order wavefunction of a system is expresse d as an asymmetric product of strong-orthogonal geminals (APSG), moreo ver, many-order correction wavefunctions are constructed to describe t he correlation interactions among several bonds. As an application, a Heitler-London-like function was chosen as the bonded function to perf orm the calculation of methane molecule. The results show that the fir st to the third correction energies consist in an approximate ratio of 4:2:-1. Thus the convergence of the correction wavefunctions is moder ately good.