Force Constants in Hartree–Fock Theory

Abstract

Force constants in Hartree–Fock (HF) theory are examined in view of the fact that they are predicted to be good through first order in the wavefunction, but are usually found to be in error by more than is “typically” found for one‐electron operators. It is shown that the evaluation of force constants by the differentiation of HF potential‐energy curves is formally equivalent to their calculation at a single internuclear distance by the use of the fully coupled HF‐perturbation calculation of the requisite second‐order‐type expression (the relaxation contribution).