Multireference configuration interaction
In quantum chemistry, the multireference configuration interaction method consists in a configuration interaction expansion of the eigenstates of the electronic molecular Hamiltonian in a set of Slater determinants which correspond to excitations of the ground state electronic configuration but also of some excited states. The Slater determinants from which the excitations are performed (and which are chosen by the user) are called reference determinants. The higher excited derterminants are then chosen by the program according to some perturbation theoretical ansatz according to a threshold provided by the user.
This method has been implemented first by Robert Buenker and Sigrid D. Peyerimhoff in the seventies under the name Multi-Reference single and Double Configuration Interaction (MRDCI).