In this work, we follow a different route to obtain converged values in the CBS limit by evaluating the MP2 correlation energy in a converged plane wave basis set. Plane waves (PWs) have the advantage of forming an orthogonal basis, the completeness of which is established regularly and monotonically with the increase of a single parameter, the kinetic energy cutoff, regardless of the level of theory employed. Since the basis functions are fixed in space rather than being located at atomic centers, there is no BSSE from the outset, and the BSIE is systematically and progressively reduced to reach the ultimate intrinsic level of precision achievable by the quantum chemical method itself. In contrast, PWs generally describe explicitly only valence electrons in order to reduce the number of basis functions and keep computational cost in store, with pseudopotentials replacing the effects of the core electrons in accommodating the variations of the wave function near the nuclei that would require the inclusion of rapidly varying basis functions, i.e. high energy cutoffs leading to computationally unfeasible basis set sizes. Even if pseudopotentials are employed, a PW calculation can necessitate a number of basis functions of up to a few hundred times that of GTOs (typically of the order of 10 5 PWs) for a similar level of convergence with respect to the basis set limit, thus requiring a highly-optimized parallel implementation .