G values of the pair densities (Eq.8) for calculating the integrals over N ρ ia G ∼ 10 4 -10 5 integrands (Eq.7) as well as the contribution of ∼ 10 9 -10 11 ijab sums (Eq.9), so that only a parallel approach can handle such intense RAM and CPU requirements in a reasonable time. The PW/pseudopotential MP2 method used herein has been developed and implemented in the CPMD program for which we give the pseudocode of the parallel implementation in the Supplementary Material (Algorithm 1).