====== Atoms are the soft balls ======

The most commonly used [[http://en.wikipedia.org/wiki/Lennard-Jones_potential|Lennard-Jones]] potential.


E = A/r<sup>12</sup> - B/r<sup>6</sup>

{{:lj.png?250}} at A = 1, B = 1

A and B parameters are determined by fitting the models of liquids to experimental data ([[OPLS]]).

In the absence of such possibility they are using quantum mechanics, but do not expect the accuracy above 5-10%.