where E(d) is the total energy of the system with the water at a distance d = 3.37 from the graphene monolayer, and E(d far ) is the energy of the non-interacting system, with the water molecule at a distance d far = 7.395 from the graphene layer. A 4 × 4 graphene sheet is employed, containing 32 carbon atoms, with a vacuum gap of 14.79 Åto ensure that the monolayer does not interact with its periodic image. HF orbitals are expanded in a plane-wave basis within the PAW framework using a cutoff energy of 500 eV, as implemented in the VASP code. For the correlated calculations we use frozen natural orbitals (FNOs) computed at the MP2 level. . The number of virtual orbitals is truncated by selecting the N v FNOs with the largest occupation number.