,n which greatly accelerates the energy convergence compared to individual extrapolations. This allows to set smaller n max virtual orbitals to be diagonalized and processed in the MP2c double summation, and thus drastically reduces the computational requirements. No significant difference (> 0.001 kcal/mol) was observed if the extrapolation is done as a function of n -1 or ε -3/2 n , the latter eigenvalues corresponding to the dimer being therefore used. Extrapolation points are spaced by an increment of 100 virtual orbitals and a better accuracy is obtained with a linear fit according to