Full Configuration Interaction

Full Configuration Interaction, often abbreviated as FCI, is a computational approach used by chemists to describe the quantum state of electrons in a molecule as accurately as possible within a chosen set of atomic orbitals. It works by writing down every conceivable way that the available electrons can be arranged among those orbitals – each arrangement known as a Slater determinant – and then allowing the electrons to mix among all these arrangements. By solving for how these determinants combine, the method yields an energy and wavefunction that are exact for the given orbital basis, leaving no room for approximations in the electronic correlation.