However, the term containing the triply excited diagrams is, still, not included in this approximation, and has to be added a posteriori. The simplest way to do this is to evaluate the E replaced by their converged counterparts, similarly to what was proposed by Williams et al. The Eqs. ( ) with ( ) can be viewed as an improvement over standard expression for SAPT accurate to the second-order in the intramonomer correlation, since they account for certain classes of diagrams summed to the infinity.