Calculation of interatomic decay widths of vacancy states delocalized due to inversion symmetry

In a recent publication [J. Chem. Phys. 123, 204107 (2005)], we have introduced a new ab initio approach for the calculation of the widths of interatomic electronic decay of inner-shell vacancies in clusters. The new technique is based on the configuration interaction formalism first introduced for the description of resonance states by Fano [Phys. Rev. 124, 1866 (1961)] and on a Green function method for the description of the many-electron states involved in the electronic decay. Central to the new method is the selection of the physical excitation operators for the construction of the initial and final states of the interatomic decay. The previously described selection procedure has been formulated for localized vacancy states and runs into difficulties when applied to the decay of vacancy states delocalized due to inversion symmetry, e.g., (2s(-1)) 2Sigma(g,u)+ states of Ne2+. Here we present a modified computational scheme suitable for interatomic decay of the energy-split gerade and ungerade states and apply it to the interatomic Coulombic decay in two homonuclear diatomic clusters: Ne2 and Ca2.