Multi-configurational self-consistent field (MCSCF) is a method in
quantum chemistry used to generate qualitatively correct reference states of molecules in cases where
Hartree–Fock and
density functional theory are not adequate (e.g., for molecular ground states which are quasi-degenerate with low-lying excited states or in bond breaking situations). It uses a linear combination of
configuration state functions (CSF) or configuration determinants to approximate the exact electronic
wavefunction of an atom or molecule. In an MCSCF calculation, the set of coefficients of both the CSFs or determinants and the basis functions in the molecular orbitals are varied to obtain the total electronic wavefunction with the lowest possible energy. This method can be considered a combination between
configuration interaction (where the molecular orbitals are not varied but the expansion of the wave function) and Hartree–Fock (where there is only one determinant but the molecular orbitals are varied).