CNDO/2-FPP atom-in-molecule polarizabilities

Abstract

The finite perturbation (FP) method of obtaining molecular and atom-in-molecule polarizabilities from the semiempirical CNDO/2 algorithm has been extended by the addition of parametrized polarization orbitals (PO) (2p for H, 3d for C, N, O, F, P, S, Cl, and 4d for Se and Br). The new parameters in CNDO/2-FPP are a screening constant for the off-diagonal core Hamiltonian terms, the PO orbital exponent, and, for the heavier elements, the PO electrongativities and the resonance integral. The parametrization preserves the charge distribution and the occupied molecular orbitals, and is designed to fit 13 model molecules; it obtains extra polarizability from the new hybrid contributions to the dipole moment and from reshuffling the virtual molecular orbitals. Excellent molecular and atom-in-molecule polarizabilities are obtained, for 47 other molecules, in agreement with available experimental data, and in competition with the best ab initio calculations.