It is important to mention that there also exist specialized approaches based on the relative ∆∆G calculations to evaluate free energy differences for structurally highly distinct ligands and different binding poses, e.g. separated topolgy method . Using the relative free energy calculations has the advantage of avoiding the requirement to properly represent protein's apo state, as this state is not explicitly considered. Yet, absolute binding free energy protocol offers a number of additional possibilities. For example, estimation of the absolute ∆G makes it possible to evaluate ligand selectivity against different protein targets, evaluate affinity for various protein conformers, calculate binding affinities for individual molecules without the need to consider them in a relation to other ligands.