Molecular properties from coupled-cluster Brueckner orbitals

We investigate to which extent a single determinant made up from orbitals o btained by a Brueckner coupled-cluster doubles calculation is able to repro duce correlated one-electron properties. It is shown that dipole and quadru pole moments and radial expectation values compare quite well with BCCD fin ite-freld results for a test selection of nine molecules enclosing HF, H2O, NH3, CO, N-2, NO+, HCN, CuH and CH3OH and three rare-gas atoms He, Ne and Ar. Furthermore, we find that even second-order properties such as dipole a nd quadrupole polarizabilities are reproduced fairly well when determined a s first derivatives of the corresponding Brueckner orbital expectation valu es. (C) 1999 Elsevier Science B.V. All rights reserved.