The bonded tableau is expanded in a series of bonded functions of different order, where the zeroth-order wave function of a system is expressed as an asym. product of strongly-orthogonal geminals (APSG); moreover, many-order correction wave functions 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 mol. The results show that the first to the third correction energies consist in an approx. ratio of 4:2:-1. Thus, the convergence of the correction wave functions is moderately good.

Key words: METHANE, FUNCTION, UNITARY GROUP APPROACH, CORRELATION ENERGY