Breit-Pauli and intermediate-coupling collision strengths for the correlation resonances that arise in the electron-impact excitation of Ni4+

We present the results of R-matrix Breit-Pauli and intermediate-coupling frame transformation (ICFT) calculations for the electron-impact excitation of Ni4+ at low energies. We focus on the correlation resonances due to the 3p(5)3d(8) configuration, which are a severe test of the ICFT method. We observe differences between the results of the two methods for the detailed shape and position of the broad correlation resonances but the effect of using the Breit-Pauli method is mainly redistributive, except for extremely weak transitions. This observation, together with our previous findings (Griffin et al 1998 J. Phys. B: Ar. Mel. Opt. Phys. 31 3713-27), means that the ICFT method is expected to be an accurate way of allowing for relativistic effects in the electron-impact excitation of complex ions, particularly for rate coefficients for the spectroscopic modelling of astrophysical plasmas.