Multireference configuration interaction

Multireference Configuration Interaction (MRCI) is a sophisticated computational chemistry method used to account for electronic correlation in molecular systems, particularly when dealing with situations where single-reference methods (like Configuration Interaction, CI, or Hartree-Fock) fail to adequately describe the electronic structure. This typically occurs in systems where there are multiple nearly-degenerate states or when the system exhibits strong correlation effects, such as in transition states, excited states, or systems with open shells.