THE RELATIVISTIC COUPLED-CLUSTER METHOD - TRANSITION ENERGIES OF BISMUTH AND EKA-BISMUTH

The relativistic coupled-cluster method, which incorporates relativist ic terms through second order in the fine-structure constant a and cor relation effects summed to all orders of the one- and two-electron exc itations, is described. An application to the transition energies of b ismuth and eka-bismuth (element 115) is described. A large basis (34s2 6p20d14f9g6h4i) is used to solve the Dirac-Fock-Breit equations, and t he external 37 electrons of each atom are then correlated. Good agreem ent with experimental values is obtained for Bi, with an average error of 0.05 eV. Two bound states are predicted for the Bi- anion. The tre nd of transition energies upon going from Bi to eka-bismuth shows a re lative stabilization of the p(1/2) orbital and destabilization of p(3/ 2) in the heavier element, by 1.5-1.9 eV per electron.