Fully relativistic density functional calculations of the ground and excited states of Yb, YbH, YbF, and YbO

摘要

Fully relativistic density functional calculations using the recently developed Beijing 4-component density functional program package (BDF) were performed for a large number of excited states of the ytterbium atom and the spectroscopic constants of the ground and some excited states of the diatomic molecules YbH, YbF and YbO. It is shown that in a relativistic framework based on the Dirac-Coulomb Hamiltonian modern (nonrelativistic) density functionals work fairly well even for the rather compact 4f shell, i.e., they quantitatively reproduce the excitation energies due to the occupation changes in the 4f shell, in contrast to previous statements made by other authors. The nondegeneracy induced by the approximate density functionals to the degenerate open 4f shell is found to be almost independent of the occupancy of outer shells as well as Hund's coupling and of the same order as that fur the first transition metals. After subtracting the unphysical nondegeneracy we obtain reasonable patterns of excited states due to different occupations of the 4f spinors for the molecules studied here. Although the spectroscopic constants for YbH and YbF obtained by this and other theoretical work are all in good agreement with available experimental data, the theoretical results for YbO show remarkable disagreement with each other and experiment. The present calculations favor a Omega = O+ ground slate with a leading f(14)sigma(o) configuration, which is in agreement with the interpretation of experimental data. (C) 1998 American Institute of Physics. [References: 91]