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 |