OPEN-SHELL RELATIVISTIC COUPLED-CLUSTER METHOD WITH DIRAC-FOCK-BREIT WAVE-FUNCTIONS - ENERGIES OF THE GOLD ATOM AND ITS CATION

The relativistic Fock-space coupled-cluster method for the direct calc ulation of ionization potentials and excitation energies (including fi ne structure) is presented and applied to atomic Au and its ions. The no-pair Dirac-Coulomb-Breit Hamiltonian is taken as the starting point . The CCSD approximation is implemented (where CCSD indicates coupled cluster with single and double excitations), which includes single and double virtual excitations in a self-consistent manner, incorporating therefore the effects of the Coulomb and Breit interactions to all or ders in these excitations. A rather large basis set (21s 17p 11d 7f) o f kinetically balanced Gaussian spinors is used to span the atomic orb itals. All calculated energies (ionization potential and electron affi nity of Au, excitation energies of Au and Au+) agree with experiment t o 0.1 eV or better, with an average error of 0.06 eV. Fine structure s plittings are accurate to better than 0.01 eV.