The applicability of the MSXα method to the lanthanides

Multiple scattering Xα (MSXα) calculations have been performed on the lanthanide trihalide molecules: LaF₃, LaCl₃, CeF₃, CeCl₃, PrCl₃, EuCl₃, GdCl₃, TbCl₃, YbCl₃, and LuCl₃. Both spin restricted (SR) and spin polarized (SP) calculations were done for all of the open shell molecules except CeF₃ for which only SR results were obtained. The closed shell molecules were treated only in an SR format. An overlapping atomic sphere model was used in all cases except EuCl₃, for which both overlapping sphere and nonoverlapping sphere models were employed. Both neutral molecule calculations and transition state calculations (0.5 an electron removed) were carried out for all molecules except the nonoverlapping sphere EuCl₃ and the SP YbCl₃, for which results were obtained only for the neutral molecules. The primary emphasis of the work was to assess the effectiveness of the MSXα method in adequately describing the behavior of the 4f electrons. These electrons are expected to exhibit: (1) valence region energies, (2) only small crystal field splittings, and (3) only slight participations in bonding.

The SR calculations predicted the above type of behavior for the 4f electrons in molecules containing zero or only one or two unpaired 4f electrons. However, in molecules containing six or seven unpaired 4f electrons the SR results indicated a rather substantial involvement in bonding and significant crystal field splittings for these electrons. For these molecules the SP calculations greatly improved the results by reducing both the participation in bonding and the crystal field splittings of the 4f electrons.