Automated incremental scheme for explicitly correlated methods

An automated implementation of the incremental scheme for the computation of MP2-F12 and CCSD(F12) energies is presented. The numerical accuracy of the approach is explored for a set of 15 chemical reactions using the limiting case of single orbital one-site domains as a worst case scenario. The results are analyzed by the maximum absolute deviation, the mean absolute error, and the root mean square error, with respect to the standard MP2-F12 and CCSD(F12) results. It is found that the MP2 reaction energies are within 1 kcal/mol accuracy at third order of the expansion, whereas the F12 corrections are already sufficiently accurate at second order. For the CCSD(F12) method 1 kcal/mol accuracy is obtained at fourth order. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3394017]