An efficient reformulation of the closed-shell coupled cluster single and double excitation (CCSD) equations

Abstract

The closed-shell CCSD equations are reformulated in order to achieve superior computational efficiency. Using a spin adaptation scheme based on the unitary group approach (UGA), we have obtained a new set of equations that greatly improves our previous formulation. Based on this scheme we have also derived equations for the closed-shell configuration interaction including all single and double excitations (CISD) case. Both methods have been implemented and tested. For a range of test cases the new CCSD method is more efficient than the earlier CCSD method. The new closed-shell CISD procedure is faster than the shape-driven (SD)GUGA algorithm and the new CCSD scheme is less than two times more computation intensive than SDGUGA CISD per iteration.

Quantum Monte Carlo study of the ground state and low-lying excited states of the scandium dimer

“…For both the CCSD͑T͒ and CASPT2 calculations, the TZVP-G͑3df ,2p͒ basis set described above were used. CCSD͑T͒ is a coupled-cluster method, 42,43 which uses single and double excitations from the Hartree-Fock determinant, [44][45][46][47] and includes triple excitations noniteratively. 48 Finally, CASPT2 ͑Refs.…”

Sensing mechanism for a fluoride chemosensor: invalidity of excited-state proton transfer mechanism

“…Second, single-point energy calculations, based on the self-consistent reaction field approach and IEF-PCM (THF, e = 7.43), were performed at the optimised gas-phase geometries to consider the solvent effect. For a benchmark comparison, single-point energy calculations were further performed using the RI-CC2 method 36,37 with the same TZVP basis set (gas phase) and the coupled cluster singles and doubles (CCSD) method 42 with the same TZVP basis set (solvent, IEF-PCM, THF, e = 7.43). The CCSD calculations were carried out using Gaussian 09 programs.…”

A theoretical study on the spectroscopy, structure, and stability of C2H3NS molecules

“…Next, coupled-cluster computations (CCSD [40][41][42] with the cc-pVTZ [34,35] basis set) were performed to improve the precision of molecular geometry predictions. Equilibrium electric dipole moment values were obtained at the same level of theory.…”