Accurate calculation of core-electron binding energies: Multireference perturbation treatment

The determination of core-electron binding energies (CEBE) of atoms and molecules, was described using multireference perturbation theory (MRPT) with multiconfigurational self-consistent field (MCSCF) reference functions. The orbital relaxations in a core-ionized state and electron correlation were considered in a conventional MCSCF-MRPT procedure. The target core ionized state was directly optimized as an excited state and this treatment completely prevented a variational collapse, in the MCSCF calculation. The results show that CEBE can be applied to higher angular momentum orbitals by including spin-orbit coupling.