The convergence of post-HF energies with respect to the number of GTO basis functions is markedly slower than it is for HF or DFT. This is attributed to the need of large atomcentered bases to fully accommodate the asymptotic behavior of the wave function around the electron-electron cusp . For PWs associated with effective pseudopotentials, we observe that the value of E ϕ cut that converges relative HF energies is in general close that required for recovering most of the MP2c contribution, and both require a fairly large N G . In contrast to atom-centred bases, the sluggish convergence of the MP2 energy in PWs is rather reflected in the progression of the sum