Eq. ( ) is the main result of this paper. With the Eq. ( ) it relates the dispersion energy to the cluster operators of the monomers, and the operator σ. The Eq. ( ) is linear in σ and is analogue to the equation for the first-order Ω operator in the coupled cluster response theory, but with similarity-transformed two-electron intermolecular Coulomb operator as non-homogeneity. Note also that the above equations gives the nested commutator which is finite. To this point we have not introduced any truncation to the T C nor S C operator and, as such, this equation is very general. The derivation of explicit orbital expressions for the Eqs. ( ) and ( ) is possible, thought involves very tedious algebra, even when the wavefunctions of the monomers are at the level of CCSD. These equations are, however, a good starting point for approximate schemes, as the error in W can be controlled at desired level. Thus, the theory provides opportunity to define a systematically improvable family of approximations to above equation.