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The effective core potential (ECP) method is modified to include frozen orbitals in order to improve the description of the outer core-valence interactions. Applications are made to the Sc, Ni and Pd atoms and several compounds containing these. It is shown that the new ECP resolves the earlier problems concerning the bond distance in ScO(²Σ⁻) and the rotational barrier in [NiH₄]²⁻. At the MC and CI levels the ²Δ and ²Π states of NiH are accurately described using the new type of ECP.