A simple, approximate method of simultaneously handling the 5s and 6s valen
ce orbitals of the lanthanide elements in Wood-Boring based relativistic ab
initio core model potential calculations (WB-AIMP), which had previously b
een formulated with the restriction of having only one valence orbital with
a given l, is presented. Its applicability is shown in spin-orbit configur
ation interaction calculations on Ce and spin-free calculations on CeO. The
good quality of the Wood-Boring spin-orbit operators oi Ce is shown and a
recommended contraction of its valence basis set is established. These resu
lts support the production of WB-AIMP data for the lanthanide series. (C) 1
999 Elsevier Science B.V. All rights reserved.