Relativistic effects, core polarisation and relaxation in ionisation potentials along Rb and Cs isoelectronic sequences

Abstract

In order to assess the relative importance of the relativistic effects, core polarisation and relaxation in ionisation potentials for Rb through Mo5+ and Cs through Pr4+ the single-configuration relativistic Hartree-Fock ionisation potentials have been computed in the 'frozen-core' and 'relaxed-core' approximations with and without allowance for core polarisation. The relativistic effects are studied by comparing the non-relativistic and relativistic Hartree-Fock data, and polarisation of the core by the valence electron is included by introducing a polarisation potential in the one-electron Hamiltonian of the valence electron. The core polarisation potential depends on two parameters, the static dipole polarisability of the core alpha and the cut-off radius r0, which are chosen independently of the ionisation potential data. Both relativistic and core polarisation effects have essential influence on the ionisation potentials of s, d and f states, whereas the core relaxation is important for the d and f states only. By including relativistic effects, core polarisation and relaxation in the single-configuration Hartree-Fock ionisation potentials it is possible to achieve an average agreement with experiment of around 1-2%.