Transferability in the natural linear-scaled coupled-cluster effective Hamiltonian approach: Applications to dynamic polarizabilities and dispersion coefficients.

A natural linear-scaled coupled-cluster (CC) method has been developed to calculate the response properties of large molecules, for example, dynamic polarizabilities and dispersion coefficients. The method is based on the transferability of the CC effective Hamiltonian from the equation-of-motion (EOM)-CC methods, subject to its representation in terms of highly transferable natural localized molecular orbitals. This transferability allows the interactions among regions in a molecule to be classified according to their important inter-region excitations and de-excitations. Dynamic polarizabilities determined in this way provide insight into calculating the excited states of large molecules using localized orbital concepts. Dispersion coefficients for the interactions within large molecules can be similarly determined. These could be useful in constructing corrective long-range potentials. Applications to alkanes, tryptophan, and polyglycine are presented. For those cases which are possible, conventional results can be reproduced. Dynamic polarizabilities of tryptophan indicate that the first excited state is localized to the indole group, while the second is localized to the carboxyl group.