As a result, the gradual convergence of GTOs toward PW values validates both the MP2 implementation in CPMD as well as the previously proposed extrapolation procedure to compute PW interaction energies in the CBS limit (Section IV A). Furthermore, our results highlight the importance of diffuse basis functions needed to incorporate the long-range components of the electron correlation in weakly bound systems , and in this respect provide further confirmation of the use of (aug-)cc-pVXZ bases for converging binding/interaction energies with correlated methods, although they were originally designed for the treatment of anions and electron affinities .