Main points: This paper concerns about the basics, as well as the capabilities and limitations of the intermolecular potential calculation. As a novice, I like the basic part better. Because the small molecules cases are easy to cope with, the author cares more about the intermolecular potential calculation between two large molecules. In this situation, the author claims, intermolecular potential calculation is transformed into pairwise atom-atom potential calculation, which is the sum of all the potentials between any of the atoms in molecule A and another one in molecule B. This can cause a double count problem but the author does not mention too much about it. The calculation of the potential is through a general-form function: U {sub a & b}, whose variables are interatomic distance R and relative orientation Omega between the two atoms involved. For the Omega (relative orientation), I think this the result of concerning the electron distribution in the electron cloud of each atoms or the partial charge distribution, which is discussed later in the paper.

There are a total of five terms contributing to the potential function: 1) the electrostatic term; 2) the exchange-repulsion term or van de Waals repulsion; 3) the dispersion term or van de Waals attraction; 4) induction term; 5) charge transfer term. (1) For the electrostatic term, the author reviewed several methods that involve charges, dipoles, multipoles, etc, instead of using point charges. And, truly, these methods can interpret the electrostatic term better, especially in the hydrogen-bonded systems. (2) For the exchange-repulsion term, according to the author, the Born-Mayer form works better than the R {superscript -12} term in the Lennard-Jones potential. (3) As for the dispersion term or van de Waals attraction, it is calculated through a series with a introduction of a correction term (a damping function) for R near zero. (3) The induction term and charge transfer term are the most troublesome ones, from the perspective of the author. The induction term comes from the interaction between an electric-field-giving atom and the consequent induced dipole of another atom. The charge transfer term is caused by the donating of electron density of one atom to the acceptor molecular orbital (MO) of another atom (maybe I should say the MO of another molecule), which will give rise to charges in electron configuration. There are two ways of dealing with this induction term: inexplicit induction, by modifying the properties of each molecule and explicit induction, by assigning isotropic dipole-dipole polarizabilities to atoms and repeating solving induction term at each step during the optimization or simulation.

Up until now, it is already practical to accurately calculate the interatomic potentials for small molecules (using, say, ab nitio method) and molecules made up of 20-30 atoms (using, say, symmetry-adapted perturbation theory based on DFT). For macromolecules, the simplest way is employing atomic point charges, Lennard-Jones or Born-Mayer repulsions, and isotropic atom-atom dispersion, while other treatments are also available. However, there is currently no definitive all-purpose force field.

Two limitations are associated with intermolecular potential calculation. One is the difficulty in describing flexible molecules. The other is the limited available experimental data for the use of parametrizing the force field.

Generally, this is a good review of the development of intermolecular potential calculation and it is appropriate for all level reader interested in this field.

References:

Stone, Science, 321, 787-789, 2008.