Knowledge Bank

The effective valence shell Hamiltonian ($H\nu$) method is used to compute the true $\pi$-electron parameters of a number of small, conjugated molecules. These true parameters are used to test several fundamental assumptions of Semiempirical $\pi$-electron, such as the zero-differential-overlap (ZDO) approximation, the transferability of parameters, and the role of three - and four electron interaction. The true electron perpendicular display remark able transferability between different molecules, and corrections to the ZDO approximation are evident. The role of three and four electron parameters are interpreted for the low lying spectra.