Computations of intermolecular interactions: Expansion of a charge‐transfer energy contribution in the framework of an additive procedure. Applications to hydrogen‐bonded systems

A procedure is given to derive an explicit charge‐transfer contribution from the Murrell–Randic–Williams formula, and to implement it in the framework of an additive procedure for the computation of intermolecular interaction energies, as a sum of electrostatic, repulsion, polarization, dispersion, and charge‐transfer terms. Comparisons are performed between the radial and angular dependence of this term in model hydrogen‐bonded systems, and that of the charge‐transfer term resulting from SCF supermolecule computations. The evolution of the derived term can be matched very satisfactorily to that of an SCF counterpart when the counterpoise correction is taken into account. The underlying features governing the radial and angular evolution of the counterpoise and charge transfer terms are underlined.