Ab initio all-electron fully relativistic Dirac—Fock self-consistent field calculations for UCI6

Abstract

Ab initio all-electron fully relativistic Dirac-Fock and non-relativistic Hartree-Fock self-consistent field (SCF) calculations are reported at four UCl bond distances, assuming octahedral UCl6. The results are fitted to a polynomial, obtaining thereby the optimized values of the bond distance and the corresponding total electronic energy for the UCl6. The nonrelativistic Hartree-Fock (HF) and Dirac-Fock (DF) SCF calculations predict UCl6 to be bound, with a predicted dissociation (atomization) energy D e of 11.88 eV and 17.89 eV, respectively. Relativistic effects lead to ~51% increment in the predicted atomization energy of UCl6. The UCl bond lengths predicted for UCl6 with the relativistic DF and non-relativistic HF wave-functions are 2.46 Å and 2.58 Å, respectively. Complete neglect in the SCF step of the two-electron [SS|SS] integrals involving the small components of the spinors (NOSS) in the DF SCF calculation for UCl6 predicts a D e of 18.25 eV and essentially the same bond length (2.48 Å) as that predicted with the full SCF procedure. Thus the small components contribute an antibinding relativistic effect of ~0.4 eV to the D e of UCl6 and have a negligible effect on the bond length. The calculations show that relativistic effects are significant for the bonding and the dissociation (atomization) energy of UCl6, and that these may be treated accurately using Dirac's fully relativistic equation for an electron.