A practical use of self-energy shift for the description of orbital relaxation

A practical use of self-energy is proposed for the description of orbital relaxation involving excited states. The proposal is first applied to modify the energy contribution from orbital relaxation in the method of configuration interaction singles with perturbative doubles, originated by Head-Gordon et al. as CIS(D). Namely, the self-energy shift is introduced for outer valence orbital energies in the denominator of contraction formula. This modification is found to be effective for Rydberg states with keeping a balance of correction for valence states. The second application of self-energy shift concerns the polarizability which is evaluated as a linear response (LR) property. The modified polarizability values become closer to those obtained by correlated calculations.