Correlation effects in heavy multi-electron ions represented by 4-4 transitions in the Zn-like isoelectronic sequence

A model potential relativistic method is used to calculate the energies of the lower levels with configurations 4s4p, 4p2, 4s4d, 4p4d in the Zn I isoelectronic series for nuclear charges Z=36-50. The calculation is made in the first order of perturbation theory with the effective inclusion of higher corrections. The role of various correlation effects is evaluated: core polarisation due to outer electrons, superposition of configurations, mutual screening of the outer electrons. As a zeroth approximation the authors obtain the wavefunctions of the outer electron in the field of the core model potential; the model potential parameter being determined from the empirical energy levels of Cu-like ions. An extrapolation procedure for model potential parameters is used for the calculation of energy levels of Cu-like ions. Energy levels 4lj and 5lj of Cu-like ions for Z=36-60 are given with an accuracy of about 0.1%. The accuracy of the energies of Zn-like ions is within 1%.