title: Geminal-spanning orbitals make explicitly correlated reduced-scaling coupled-cluster methods robust, yet simple.
abstract: We present a production implementation of reduced-scaling explicitly correlated (F12) coupled-cluster singles and doubles (CCSD) method based on pair-natural orbitals (PNOs). A key feature is the reformulation of the explicitly correlated terms using geminal-spanning orbitals that greatly reduce the truncation errors of the F12 contribution. For the standard S66 benchmark of weak intermolecular interactions, the cc-pVDZ-F12 PNO CCSD F12 interaction energies reproduce the complete basis set CCSD limit with mean absolute error <0.1 kcal/mol, and at a greatly reduced cost compared to the conventional CCSD F12.
authors.affiliation: Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, USA.
authors.forename: Fabijan
authors.initials: F
authors.lastname: Pavošević
authors.affiliation: Max Planck Institut für Chemische Energiekonversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.affiliation: Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, USA.
authors.forename: Edward F
authors.initials: EF
authors.lastname: Valeev