The simplest off-lattice model of the liquid is a system of spherical particles, interacting via a pairwise potential, that depends on the distance between them, . As we know, molecules repel, when they are very close to each other, but attract each other at larger separation. It is a sum of the short-range repulsive contribution and attractive contribution .
Attractive term describes the interaction between two molecules.
When two atoms are brought close to each other, charge density fluctuations in the first atoms's electron shell induce polarization of the electron shell of the other. The attraction between the two induced dipoles leads to the attractive inverse sixth power term. Very similar interaction is observed between two colloid particles, or polyelectrolyte molecules, where the induced dipoles are due to the fluctuations of the counter-ion density distribution. These fluctuations and the induced electron shell polarization are described by very similar equations and therefore lead to the similar answer. But their nature is very different.