MOLLER-PLESSET EVALUATION OF THE STATIC FIRST HYPERPOLARIZABILITY OF POLYMETHINEIMINE

A finite oligomer approach is used to compute the longitudinal compone nt of the static electronic first-hyperpolarizability per unit cell (D elta beta(L)(N)) of polymethineimine. The longitudinal first hyperpola rizability (beta L) is calculated accounting for electron correlation effects via the Moller-Plesset partioning. The influences of the basis set size, of the order in electron-electron interactions up to which the electron correlation effects are accounted for and of the modifica tion of the equilibrium geometry due to the inclusion of electron corr elation are considered. Contrary to the Hartree-Fock level for which D elta beta(L)(N) vs. N firstly presents a minimum then increases toward s its polymeric value, at the MP2 level, Delta beta(L)(N) evolves mono tonically with chain length and its asymptotic value is 7.7 times larg er than the CPHF results reaching the large value of 4.2 X 10(-30) esu g(-1) mol. (C) 1998 Elsevier Science B.V.