The relativistic open shell coupled cluster method: Direct calculation of excitation energies in the Ne atom

Publisher Website
Google Scholar
Abstract
The relativistic Fock space coupled‐cluster method for the direct calculation of excitation energies (including fine structure) is presented and applied to excitations of atomic Ne. The coupled clusters with single and double excitations (CCSD) approximation, which includes single and double virtual excitations in a self‐consistent manner, is implemented. The no‐pair Dirac–Coulomb Hamiltonian is taken as the starting point. Mean length basis sets of balanced Gaussian spinors are used to span the atomic orbitals. The model (P) space is quasicomplete, consisting of determinants with one valence hole and one valence particle. Fourteen excitation energies of the atom are calculated. They all agree with experiment to 0.08 eV or better, with an average error of 0.02 eV. Fine structure splittings are also in very good agreement with experiment.