REDESIGNING SEMIEMPIRICAL-LIKE PI-ELECTRON THEORY WITH 2ND-ORDER EFFECTIVE VALENCE SHELL HAMILTONIAN (H-V) THEORY - APPLICATION TO LARGE PROTONATED SCHIFF-BASES

The fast and simple second order effective valence shell Hamiltonian ( H-nu) method is applied to the series of protonated Schiff bases (C=C- )(n)C=NH2 + for n = 1, 5, generating ab initio analogs of the pi-elect ron effective integrals alpha(i), beta(i,j) and gamma(i,j) that appear in the semiempirical Pariser-Parr-Pople (PPP) theory. The H-nu beta(i ,j) and gamma(i,j) transfer remarkably well between all five Schiff ba ses. The other non-negligible effective integrals constitute only a mi nute fraction of the matrix elements of the H-nu two- and three-electr on operators and also transfer exceptionally well. The present calcula tions set the stage for developing an ab initio PPP model applicable t o these and other biological interesting chromophores.