Energy levels and oscillator strengths for Mg-like copper

•Energies and transition rates for the lowest 185 levels in Cu XVIII are reported.•The MBPT and MCDF methods are employed to include the many-body effects.•The most accurate and complete atomic data in Cu XVIII are provided to date.

Energy levels and oscillator strengths for electric-dipole (E1), electric-quadrupole (E2), magnetic-dipole (M1), and magnetic-quadrupole (M2) transitions among the lowest 185 levels arising from the n≤5 configurations in Cu XVIII are calculated through second-order many-body perturbation theory (MBPT). To illustrate the improvement of many-body perturbation corrections, we have also carried out the parallel calculations using the standard relativistic configuration-interaction (RCI) approach. Furthermore, to confirm the accuracy of the present MBPT results and show further the importance of valence-valence and core-valence correlation effects, we have performed another independent calculation using the multiconfiguration Dirac-Fock (MCDF) method within the GRASP code in the active space approximation. The accuracies of the present level energies, wavelengths, transition rates and lifetimes are assessed by comparing to available experimental and other theoretical results. The present MBPT and MCDF results are believed to be the most comprehensive and accurate ones to date.