Dispersion energy of symmetry-adapted perturbation theory from explicitly correlated F12 approach

Methods of the explicitly correlated F12 approach are applied to the problem of calculating the uncoupled second-order dispersion energy in symmetry-adapted perturbation theory. The accuracy of the new method is tested for noncovalently bound complexes from the A24 data set [J. \v{R}ez\'{a}\v{c} and P. Hobza, J. Chem. Theory Comput. 9, 2151 (2013)] using standard orbital basis sets aug-cc-pV$X$Z supplemented with auxiliary aug-cc-pV$X$Z_OPTRI sets. For near equilibrium geometries, it is possible to recover the dispersion energy with average relative errors consistently smaller than 0.1% (with respect to the CBS extrapolated limit estimated from regular orbital calculations). This level of accuracy is achieved already in basis set of a triple-zeta quality, when a Slater-type correlation factor $\exp(-0.9\,r_{12})$ is combined with variant C of the F12 approach. The explicitly correlated approach clearly outperforms regular orbital calculations in the basis set of 5-zeta quality (average relative errors of 1%).