Time-dependent perturbation calculation for the doubly excited states in two-electron systems

Abstract A new but simple method based on time-dependent perturbation theory has been proposed to study the doubly excited states of two-electron systems. The method essentially seeks the natural excitation modes of the two-electron charge cloud. A test calculation for two such states of H − , He and Li + yields reasonably accurate excitation energies and excited state wavefunctions. A possible extension of the theory to many-electron systems is proposed.