Coupled-cluster response theory: Parallel algorithms and novel applications

The parallel implementation of coupled-cluster response theory within NWChem and its subsequent application to novel chemical problems is reported. Linear-response dipole polarizabilities of polyacenes, the 60-carbon buckyball, and larger water clusters were computed with coupled-cluster singles and doubles (CCSD) and compared to density-functional results. The complete treatment of coupled-cluster response theory including up to triples (CCSDT) was applied to diatomic molecules using large basis sets and this method was used to evaluate a newly-developed perturbative approximation for triples. Hyperpolarizabilities and Lennard-Jones coefficients were implemented at the CCSD level of theory by extending the linear response code in two different ways. Benchmark hyperpolarizabilities are reported for molecules as large as para-nitroaniline using large basis sets. Tensor transpose algorithms are shown to be an important component in a coupled-cluster property code and automatic code generation successfully identified faster algorithms for these.