The calculation of second-order molecular properties at the configuration interaction level of accuracy

Abstract

It is argued that the calculation of second-order properties, such as electric polarisabilities and magnetic susceptibilities, at both the Self-Consistent Field (SCF) and Configuration Interaction (CI) levels of accuracy, should be determined by perturbation theory rather than via the finite field approach. The SCF perturbation equations are discussed for both closed- and open-shell systems. Furthermore, to demonstrate the method, the first-order perturbation equations are solved at the CI level to give the electric polarisability tensor of water.