CCSD, CCSD(F12) and CCSD(T) calculations

CCSD, CCSD(F12) and CCSD(T)

The ricc2 module includes presently also initial implementation of the full coupled-cluster singles-and-doubles method CCSD, explicitly correlated CCSD(F12) variants and of CCSD with a perturbative correction for connected triples, CCSD(T). Presently the implementation is restricted to ground state energies. Closed-shell (RHF), unrestricted (UHF) or single determinant restricted (ROHF) open-shell reference wavefunctions can be used, but no excitation energies, gradients or properties are (yet) available for these wavefunction models.

Further limitations:

no symmetry treatment

, all calculations at these levels must presently done in C₁ symmetry

no parallelization

, calcualtions at these levels can presently only carried out on a single processor (core)

Please note that calculations with CCSD and methods beyond CCSD require considerably more disc space and core memory than MP2 or CC2 calculations. (See section below for more details and recommendations.)