exch-ind and E (20) exch-disp , were calculated in S 2 and S 4 approximations as well as without approximation of permutation operator, using new second quantization expressions. As the reference for these values, the above-mentioned corrections were also calculated in an unapproximated form using the well-known density matrix approach. In all calculations, the intramolecular correlation effects have been neglected. For construction of the unperturbed wavefunctions the RHF determinants were used. All exchange energy corrections were calculated within the jun-cc-pVTZ basis set, except for the ethylene dimer, where the smaller jun-cc-pVDZ basis was used due to the system size.