Linear response functions for coupled cluster/molecular mechanics including polarization interactions

We present the first implementation of linear response theory for the coupled cluster/molecular mechanics (CC/MM) method. This model introduces polarization effects into a quantum mechanical/molecular mechanical (QM/MM) framework using a self-consistent procedure while electrostatic effects are modeled by assigning partial charges to the MM molecules and a van der Waals potential describes dispersion and short range repulsion. The quantum mechanical subsystem is described using coupled cluster electronic structure methods. The response theory for the calculation of molecular properties for such a model is described and implemented at the coupled cluster singles and doubles (CCSD) level. Sample calculations of excitation energies, transition moments and frequency dependent polarizabilities for liquid water are presented. Finally, we consider the development of a parameter independent iterative self-consistent CC/MM model where the properties calculated by CC/MM response theory are used in the QM/MM interaction Hamiltonian. (C) 2003 American Institute of Physics.