Linear response properties of liquid water calculated using CC2 and CCSD within different molecular mechanics methods

In this paper we present linear response properties of liquid water calculated using the second-order approximate coupled cluster singles and doubles (CC2) and the coupled cluster singles and doubles (CCSD) wave function parametrizations combined with different molecular mechanics models. We discuss different approaches within the QM/MM scheme where the solvent molecules are represented by point charges and induced dipole moments. Here, we address two important aspects in QM/MM methods. First, we aim at obtaining MM parameters from an iterative self-consistent approach. Second, we show how to reduce the computational costs of the models considerably without reducing the quality of the results. Excitation energies, transition moments, and oscillator strengths are compared within the different approaches. Finally, we report the CC2 frequency dependent polarizability compared to the CCSD results.