Valency electron molecular orbital calculations

A self-consistent molecular orbital perturbation method suitable for use with the CNDO/2 approximations is formulated. The first-order perturbed equation is solved with an electric field perturbation for several molecules, and the polarizabilities are obtained. The results are too low, particularly for polarizabilities along short molecular axes, with a valency orbital basis set. The inclusion of 2p orbitals on hydrogen atoms gives improved results; but it is concluded that additional basis orbitals on other atoms are required for a valid interpretation of polarizabilities.