Core effects on ionization potentials in thallium - art. no. 022507

Ionization potentials (IP's) are evaluated for various excited states of Tl using the relativistic coupled cluster (CCCD) theory in the even-parity pa ir channel approximation (CCSD-EPC). An avenge accuracy below half a percen t is reached. The effect of deep core electrons on the core-valence correla tions is investigated, It is found that electrons in the third subshell (n = 3) modify the IP's of the 6p orbitals by 100 cm(-1). By comparison with c alculations made in the linearized CCSD (LCCSD) approximation it is demonst rated that nonlinear contributions are mandatory to reach an accuracy below half a percent for the 6p(1/2) orbital.