The MP2 limit correction applied to coupled cluster calculations of the electronic dissociation energies of the hydrogen fluoride and water dimers

The basis set convergence of ab initio computed electronic dissociation energies is reported for the hydrogen bonded complexes (HF)2 (H2O)2. At the level of CCSD(T) theory (coupled cluster model with singles, doubles, and approximate connected triples), the interaction energy is split into one- and two-body terms, and corrections such as the counterpoise (CP) and the MP2 limit are explored. The MP2-limit correction consists of substituting the second-order Møller-Plesset (MP2) perturbation theory contribution computed with the actual basis set by the limiting value that is obtained in a complete basis. Clearly the basis set convergence of the CCSD(T) calculations is improved by the MP2 limit correction. Moreover, the MP2-limit correction can be applied irrespective of whether or not the two-body term has been CP corrected beforehand. Little difference is found between the two possibilities, but the most accurate results are obtained by applying the MP2 limit correction to CP corrected CCSD(T) two-body terms. Best estimates of De = 19.1(2) kJ mol-1 for (HF)2 and De = 21.1(3) kJ mol-1 for (H2O)2 are inferred.