RELATIVISTIC EFFECTS ON THE ELECTRONIC-STRUCTURE AND CHEMICAL BONDINGOF UF(6)

We have studied the relativistic effects in the electronic structure a nd chemical bonding for the ground state of UF6, using the relativisti c and nonrelativistic discrete-variational Xalpha molecular orbital ca lculations, It is found that two relativistic effects appear in the va lence levels; the energy level splitting and upward shift of energies of the molecular orbitals. From the Mulliken population analysis of th e valence levels, it is shown that the level splitting is due to mixin g of the uranium atomic orbitals with a strong spin-orbit interaction, such as U6p, and the upward shift due to the increase in the screenin g of the nuclear charge and charge redistribution. The strength of U-F bonding remarkably increases for the relativistic case, because the c hanges in the radial distributions due to the relativistic effects ind uce both the decrease in the antibonding interactions and the increase in the bonding ones.