RELAXATION AND CORRELATION CONTRIBUTIONS TO MOLECULAR DOUBLE CORE IONIZATION ENERGIES

We describe self-consistent field optimization of double core hole sta tes for single- (SCF) and multi-configuration (MCSCF) wavefunctions. W ith the proposed schemes it is possible to separate contributions to t he double core hole ionization energies due to relaxation from those d ue to correlation, and to obtain, optionally, both symmetry broken and symmetry adapted solutions of such states. Sample calculations are pe rformed to elucidate the role of single versus double core hole relaxa tion and static versus residual relaxation when the two core holes are in the same main shell but on different sites and when they are on th e same site but in different main shells. Perturbation theory results for the double equivalent core replacement species are presented and d iscussed. The ''singlet-triplet separability problem'' previously iden tified for certain double core hole states is verified and remedied by second order SCF/MCSCF.