The explicitly correlated same number of optimized parameters (SNOOP-F12) scheme for calculating intermolecular...

We augment the recently introduced same number of optimized parameters (SNOOP) scheme [K. Kristensen et al., J. Chem. Phys. 142, 114116 (2015)] for calculating interaction energies of molecular dimers with an F12 correction and generalize the method to enable the determination of interaction energies of general molecular clusters. The SNOOP, uncorrected (UC), and counterpoise (CP) schemes with/without an F12 correction are compared for the S22 test set of Jurečka et al. [Phys. Chem. Chem. Phys. 8, 1985 (2006)]-which consists of 22 molecular dimers of biological importance-and for water and methane molecular clusters. The calculations have been performed using the Resolution of the Identity second-order Møller-Plesset perturbation theory method. We conclude from the results that the SNOOP scheme generally yields interaction energies closer to the complete basis set limit value than the UC and CP approaches, regardless of whether the F12 correction is applied or not. Specifically, using the SNOOP scheme with an F12 correction yields the computationally most efficient way of achieving accurate results at low basis set levels. These conclusions hold both for molecular dimers and more general molecular clusters.