Table 1.

Overview of the most important interactions occurring between two c losed-shell electron density distributions (R is the distance between the two centers of masses)

Interaction type	Origin	Range	Directionality	Contribution
Electrostatic	Coulomb attraction/repulsion between unperturbed electron densities	Long range especially monopolar charges of ions (÷1/RL+1; where L is the sum of the multipole orders; L = 0 for charge-charge interactions)	Monopole-monopole interactions are not directional; increasing directionality for higher multipolar moments	Stabilization or destabilization, depending on the sign and orientation of the electrostatic moments of the interacting systems
Induced polarization	Coulomb attraction between electron density of one molecule and field induced polarization of the other	Shorter range (÷1/R4)	Medium-Small	Stabilization
Dispersion	Coulomb attraction between mutually polarized electron densities	Quite short range (÷1/R6)	Small	Stabilization
Short range repulsion	The reduced probability of having two electrons with the same spin very close to each other (Fermi-hole)	Very short range (÷1/R12 or exponential)	None	Destabilization
Charge Transfer	Interaction between frontier orbitals of the interacting systems it implies partial covalence	Occurs only for contacts shorter than van der Waals distances	Very high	Stabilization