On the importance of size‐consistency corrections in semiempirical MNDOC calculations

Energies obtained by configuration interaction calculations including all double excitations with regard to the Hartree‐Fock reference determinant can empirically be corrected to size consistency using either the Langhoff‐Davidson (LD) formula or a formula suggested by Pople, Seeger, and Krishnan (PSK). Semiempirical MNDOC calculations suggest that for molecular systems with a large number of electrons and important correlation effects the PSK correction is superior to the LD correction.