A STATISTICAL MULTIREFERENCE STATE-SPECIFIC DRESSING OF CONFIGURATION-INTERACTION MATRICES - APPLICATION TO HEISENBERG HAMILTONIANS

For an arbitrary (truncated or selected) configuration interaction (CI ) space and from a specific eigenvector, one may extract statistical a nd state specific amplitudes of elementary excitations. These amplitud es are used for the evaluation of the coefficients of the outer-space determinants, leading to a state specific dressing of the CI matrix. T he process is repeated to self-consistency. Numerical applications to ground and excited states of a Heisenberg Hamiltonian for conjugated m olecules illustrate the efficiency of the method.