Ionization energies and fine structure splittings of highly correlated systems: Zn, zinc-like ions and copper-like ions

The low-lying ionization energies and fine structure splittings of highly correlated systems, Zn and zinc-like ions, are computed using relativistic multireference many-body perturbation theory with large Gaussian-spinor basis sets. The relativistic multireference perturbation calculations reproduces the ionization energies of Zn and zinc-like ions to unprecedented accuracy, with the largest deviation between theory and experiment of 0.17 percent. Contributions to the ionization energy of relativity, Dirac–Coulomb and Breit correlation corrections, and the Lamb shift, are analyzed.