“…3 In particular, several sets of ECPs exist for the third-series transition metal elements. Some of them are ultimately based upon the Phillips-Kleinman equation 4 and rely on the pseudo-orbital transformation that produces nodeless valence pseudo-orbitals; this is the case of the pseudopotentials produced by Bachelet et al, 5 Hay and Wadt, 6,7 Ross et al, 8 and Andrae et al 9 Some others are based on the Huzinaga-Cantu equation 10 and lead to valence orbitals with the same nodal structure as the all-electron orbitals; this is the case of the model potentials produced by Sakai et al 11 Also based on the Huzinaga-Cantu equation, the ab initio model potential ͑AIMP͒ 12 method resulted from the implementation of two ideas which contrast with the basics of all the other ECP methods: ͑i͒ the core model potentials are obtained directly from the frozen core orbitals, without resorting to parametrization procedures based on the valence orbitals, and ͑ii͒ the components of the core model potentials must mimic the operators that they substitute as much as possible, while reducing the computing time. Accordingly, nonrelativistic AIMPs ͑NR-AIMP͒ and spin-free relativistic AIMPs derived from atomic Cowan-Griffin 13 calculations ͑CG-AIMP͒ have been produced and successfully monitored for the main-group elements, 12,14,15 and for the firstseries and second-series transition metal elements, 14,16,17 but they are not available for the third-series transition metal elements.…”