This letter proposes a relaxation scheme for core electrons based on the frozen core potential method at the infinite-order Douglas–Kroll–Hess level, called FCP-CR. The core electrons are self-consistently relaxed using frozen molecular valence potentials after the valence SCF calculation is performed. The efficiency of FCP-CR is confirmed by calculations of gold clusters. Furthermore, FCP-CR reproduces the results of the all-electron method for the energies of coinage metal dimers and the core ionization energies and core level shifts of vinyl acetate and three tungsten complexes at the Hartree–Fock and/or symmetry-adapted cluster configuration interaction levels.
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