CORRELATION IN 1ST-ROW TRANSITION-METAL ATOMS USING GENERALIZED MOLLER-PLESSET PERTURBATION-THEORY

Correlation effects in the lowest lying states arising from the 4s(2)3dn, 4s3d(n+1), and 3d(n+2) configurations of the first-row transition metal atoms, Ti, Cr, Fe, and Ni are studied using a generalized Moller-Plesset perturbation theory applicable to multiconfigurational reference wave functions. Reference wave functions including configurations describing the dominant 4s2 angular and 3d radial correlation effects are found to be essential for a perturbative treatment of these atoms. Generalized Moller-Plesset theory applied to such multiconfigurational reference wave functions gives relative energies comparable to corresponding multireference configuration interaction (CI) calculations at a lower computational cost.