Spectroscopic constants of gold and eka-gold (element 111) diatomic compounds: The importance of spin-orbit coupling

Scalar-relativistic density functional calculations in the zeroth-order reg ular approximation as well as fully relativistic Dirac-Kohn-Sham calculatio ns have been performed to investigate spectroscopic constants of the eka-go ld (element 111) compounds (111) X (X = H, F, Cl, Br, O, Au) and the dimer of element 111. For calibration, we also report results for homologous gold compounds. The bond lengths for the compounds of element 111 are similar b ut slightly larger than those of the gold compounds. Spin-orbit coupling in creases the bond length by a few pm. For the hydride and the halides, the f orce constants of the eka-gold compounds are generally larger than those of the gold compounds although the dissociation energy is smaller. The oxide of eka-gold is more strongly bound than the gold oxide. The dimer of elemen t 111 has an open shell instead of a closed-shell electronic structure and is less stable than the gold dimer. The effect of spin-orbit coupling on th e dissociation energy depends on the extent to which spin-orbit coupling is quenched in the molecule. This effect has been estimated based on a spinor occupation population analysis. (C) 1999 American Institute of Physics. [S 0021-9606(99)30304-4].