A CC2 dielectric continuum model and a CC2 molecular mechanics model

In this paper we present theory and applications for the second-order approximate singles and doubles coupled cluster (CC2) electronic structure method coupled to either a dielectric continuum (the CC2/DC model) or a molecular mechanical intermolecular force field ( the CC2/MM model). Calculations of the interaction energy, solvation energy, electric dipole moment and electric quadrupole moment of liquid water are presented using the correlated CC2 approach. The results are compared to the corresponding results using the uncorrelated Hartree-Fock (HF) and the correlated coupled cluster singles and doubles (CCSD) methods. Also, a hierarchy in the coupling between the quantum mechanical (QM) and the molecular mechanical ( MM) part of the system is investigated in the QM/MM model for the three different electronic structure methods.