Ab initio pseudopotential study of Yb and YbO

Publisher Website
Google Scholar
Abstract
Large‐scale self‐consistent‐field configuration interaction calculations with single and double excitations, multireference configuration interaction calculations, and coupled pair functional calculations using nonrelativistic and quasirelativistic energy‐adjusted ab initio pseudopotentials for Yb, together with extended basis sets, have been performed for thirteen low‐lying electronic states of YbO in the ΛS coupling scheme. Spin–orbit coupling was treated by means of energy‐adjusted ab initio spin–orbit operators in connection with quasirelativistic double group configuration interaction calculations and configuration interaction calculations with iterative perturbative selection of the zeroth‐order wave function for the twenty‐five corresponding Ω states in the intermediate coupling scheme. Controversial assignments for the YbO ground‐state electronic configuration derived from experimental facts interpreted within a ligand field model or previously published quasirelativistic pseudopotential calculations are discussed. Despite excellent results for YbH and YbF, the molecular constants of the lowest experimentally observed state of YbO (Re = 1.807 Å, D0 = 4.29 eV, ωe = 699 cm−1) recently assigned to be a 4f14σ 2σ 2π4 1Σ+ (Ω = 0+) ground state by McDonald et al. [J. Chem. Phys. 93, 7676 (1990)], show only limited agreement with the results obtained in the present work for this state (Re= 1.895 Å, D0 = 2.47 eV, ωe = 653 cm−1). In our most extensive calculations the lowest state arising from the 4f13σ 2σ 2π4σ 1 configuration (Ω = 0−) is still found to be 0.93 eV lower in energy than the 4f14σ 2σ 2π4 1Σ+ (Ω = 0+) state. The importance of differential relativistic and correlation effects in the energy separation between states arising from configurations with differing 4f occupation is demonstrated and discussed.