Relativistic and correlation effects in the ground state of atomic lawrencium

A series of multiconfiguration (MC) Dirac-Hartree-Fock (DHF) calculations were performed to study the effects of correlation on the energy difference between the [Rn]5f¹⁴7s²7p1/2, J=1/2, odd-parity (1/2ᵒ) and the [Rn]5f¹⁴6d3/27s², J=3/2, even-parity (3/2ᵉ) levels of atomic lawrencium. In particular, the effects of interactions between valence and core electrons were investigated. Single-configuration DHF calculations predict that the 1/2ᵒ level lies below the 3/2ᵉ level; the correlation effects included in the MCDHF calculation tend to reverse this ordering. For comparison, similar studies were also carried out for Y and LU, where observed related energy differences are available.