Ionization potentials and excitation energies of the alkali-metal atoms by the relativistic coupled-cluster method.

Abstract

Ground- and excited-state energies, as well as ionization potentials and electron affinities, are calculated for all the alkali-metal atoms Li--Fr by the relativistic Fock-space coupled-cluster method. The coupled-cluster singles and doubles approximation, which includes single and double virtual excitations in a self-consistent manner, is implemented. The no-pair Dirac-Coulomb-Breit Hamiltonian is taken as the starting point. Rather extensive basis sets of balanced Gaussian spinors are used to span the atomic orbitals. The average error for the ionization potentials is 0.09% and for excitation energies 0.2%. Electron affinities are less accurate, particularly for the heavier atoms, with errors of 4--9 % for K, Rb, and Cs.