Recently, an expression for the total energy that (similarly to eqn ( )) is consistent with the Hohenberg-Kohn energy functional, was derived also for methods in which the correlation energy is obtained as a nonvariational correction to variationally obtained wave functions. For whatever form of the embedded wave function, including the one introduced by Wesolowski and Warshel 579 , FDET represents a bottom-up approach to deal with the quantum embedding problem in multi-level/multi-scale simulations.