Analysis of the chemical bond

Starting from the MO-LCAO energy expression with an approximate correction for left-right correlation formalisms are derived that agree with those of some current semi-empirical schemes, but where the parameters usually fitted to experimental results are given explicitly in an ab initio way. The approximations necessary for deriving the different schemes as well as the range of their validity are discussed. For -electron systems ab initio values of the -parameters (both thermochemical and spectral) are derived.