Usually, no more than ten steps are needed to converge σ 11 . The correctness of our code could be easily checked by reproducing implemented order-by-order corrections from Eqs. ( ) - (45). For the triply excited contribution to the dispersion energy we have used existing routine from the SAPT package into which converged σ 11 and T 2 amplitudes were plugged in. The calculations of triples in dispersion is the bottleneck of the method with steep scaling of N 7 , whereas the computational cost of obtaining σ 11 amplitudes is N 6 . The implementation is preliminary, and we cannot perform the calculations for larger complexes due to the prohibitive cost of triples.