Multireference coupled cluster based analytic response approach for evaluating molecular properties: Some pilot results

In this paper we present the first results for linear response theory in the multireference Fock space framework. Dipole moments of the open shell radicals hydro peroxy radical, hydroxyl radical, and formyloxyl radical are discussed in this paper. The results obtained from the analytic response are compared with the experimental as well as the finite field results including relaxation of the orbitals and the results suggest that the effects of relaxation are substantial. The Fock space approach enables us to obtain the properties of excited states of these radicals in a single calculation. The dipole moments of the first excited states of the above radicals are also reported. The results of the lower Fock space sector energy derivatives are also presented. (C) 1999 American Institute of Physics. [S0021-9606(99)30105-7].