Dispersion Energy of Symmetry-Adapted Perturbation Theory from the 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. Rezac and P. Hobza, J. Chem. Theory Comput. 2013, 9, 2151] using standard orbital basis sets aug-cc-pVXZ supplemented with auxiliary aug-cc-pVXZ_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 the basis set of a triple-zeta quality, when a Slater-type correlation factor exp(-0.9r(12)) is combined with variant C of the F12 approach. The explicitly correlated approach clearly outperforms regular orbital calculations in the basis set of quintuple-zeta quality (average relative errors of 1%).