Finite-perturbation SCF valence-shell calculations of molecular polarizability and hyperpolarizability components

A finite-perturbation method is used for obtaining approximate valence-shell eigenfunctions of molecules interacting with uniform static electric fields within the framework of unrestricted open-shell CNDO/II theory. For a series of axially symmetric molecules, components of the polarizability tensor have been calculated. It is found that although the average polarizabilities alpha are underpredicted, the anisotropies alpha(parallel to)-alpha(perpendicular to) are remarkably well predicted by this method. Some calculation of hyperpolarizabilities beta(yyy) are also reported: these cannot yet be compared with experiment, but the result for CO is close to that of an ab initio calculation of McLean and Yoshimine. The polarizability results are also compared with infinitesimal-perturbation CXDO/II calculations of Davies.