The precise form of this potential function is a choice for which there are many options. In particular, different forms for the van der Waals interactions and the dihedrals are in common use and the bonds are often constrained in simulations. However, the form given here is reasonably general, and shows the most important assumptions that are made: only pair-additive interactions are taken into account (non-bonded interactions involving three or more atoms are neglected), atoms are represented as point charges (electronic polarizability is neglected) and simple quadratic forms are used for computational efficiency.