A general bridge between configuration interaction and coupled-cluster methods: a multistate solution

Using the concept of intermediate Hamiltonians, a state-specific dressing of an arbitrary configuration interaction matrix is presented in its full generality, proceeding through a coupled-cluster development of the desired eigenvector from its dominant single determinantal components. The method is then generalized to simultaneously search for M eigenstates through a Jeziorski-Monkhorst-type expansion from the M dominant determinants.