title: Some Observations on Counterpoise Corrections for Explicitly Correlated Calculations on Noncovalent Interactions.
abstract: The basis set convergence of explicitly correlated ab initio methods, when applied to noncovalent interactions, has been considered in the presence (and absence) of Boys-Bernardi counterpoise corrections, as well as using "half-counterpoise" (the average of raw and counterpoise-corrected values) as recently advocated in this journal [Burns, L. A.; Marshall, M. S.; Sherrill, C. D. J. Chem. Theory Comput. 2014, 10, 49-57]. Reference results were obtained using basis sets so large that BSSE (basis set superposition error) can be shown to be negligible. For the HF+CABS component, full counterpoise unequivocally exhibits the fastest basis set convergence. However, at the MP2-F12 and CCSD(T*)-F12b levels, surprisingly good uncorrected results can be obtained with small basis sets like cc-pVDZ-F12, owing to error compensation between basis set superposition error (which overbinds) and intrinsic basis set insufficiency (which underbinds). For intermediate sets like cc-pVTZ-F12, "half-half" averages work best, while for large basis sets like cc-pVQZ-F12, full counterpoise may be preferred but BSSE in uncorrected values is tolerably small for most purposes. A composite scheme in which CCSD(T)-MP2 "high level corrections" obtained at the CCSD(T*)-F12b/cc-pVDZ-F12 level are combined with "half-counterpoise" MP2-F12/cc-pVTZ-F12 interaction energies yields surprisingly good performance for standard benchmark sets like S22 and S66.
authors.affiliation: Department of Organic Chemistry, Weizmann Institute of Science , 76100 Reḥovot, Israel.
authors.forename: Brina
authors.initials: B
authors.lastname: Brauer
authors.affiliation: Department of Organic Chemistry, Weizmann Institute of Science , 76100 Reḥovot, Israel.
authors.forename: Manoj K
authors.initials: MK
authors.lastname: Kesharwani
authors.affiliation: Department of Organic Chemistry, Weizmann Institute of Science , 76100 Reḥovot, Israel.
authors.forename: Jan M L
authors.initials: JM
authors.lastname: Martin