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

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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%.