RELATIVISTIC ALL-ORDER CALCULATIONS OF ENERGIES AND MATRIX-ELEMENTS IN CESIUM

All-order methods recently developed for high-accuracy calculation of energies and matrix elements in Li are extended and applied to cesium. We employ a relativistic, linearized, coupled-cluster formalism, incorporating single, double, and an important subset of triple excitations. A coupled-cluster formulation of the matrix element of a one-body operator, incorporating the random-phase approximation exactly, is used to calculate hyperfine constants and transition-matrix elements. We find agreement with experiment at the 0.5% level or better for ionization energies and dipole-matrix elements, and at the 1% level for hyperfine constants. Modifications of the method that have the potential of higher accuracy are discussed.