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

The bonded tableau is expanded in a series of bonded functions of different order, where the zero-order wavefunction of a system is expressed as an asymmetric product of strong-orthogonal geminals (APSG), moreover, many-order correction wavefunctions are constructed to describe the correlation interactions among several bonds. As an application, a Heitler-London-like function was chosen as the bonded function to perform the calculation of methane molecule. The results show that the first to the third correction energies consist in an approximate ratio of 4:2:-1. Thus the convergence of the correction wavefunctions is moderately good.