Atomic polarizabilities and polarized pseudo-states in the multiconfigurational approach. I. Theory and application to C, N and O

The determination of polarized pseudo-states for a complex atom using LS coupling is considered. These pseudo-states are obtained by solving variationally the Schrodinger equation for the unperturbed atom and the inhomogeneous first-order perturbation equation within a superposition-of-configurations framework. This technique, which can be easily applied to any state including excited states, allows the explicit introduction of electron correlation effects in a consistent way. The pseudo-states are generated primarily for use in negative-ion and electron-atom collision calculations but they also allow accurate polarizabilities and shielding factors to be evaluated. These are calculated for C, N, and O and the results compared with those obtained from other elaborate multiconfigurational techniques.