CHARMM

Chemistry at Harvard Macromolecular Mechanics (CHARMM) is the name of a widely used set of force fields for molecular dynamics, and the name for the molecular dynamics simulation and analysis computer software package associated with them. The CHARMM Development Project involves a worldwide network of developers working with Martin Karplus and his group at Harvard to develop and maintain the CHARMM program. Licenses for this software are available, for a fee, to people and groups working in academia.

== Force fields == The CHARMM force fields for proteins include: united-atom (sometimes termed extended atom) CHARMM19, all-atom CHARMM22 and its dihedral potential corrected variant CHARMM22/CMAP, as well as later versions CHARMM27 and CHARMM36 and various modifications such as CHARMM36m and CHARMM36IDPSFF. In the CHARMM22 protein force field, the atomic partial charges were derived from quantum chemical calculations of the interactions between model compounds and water. Furthermore, CHARMM22 is parametrized for the TIP3P explicit water model. Nevertheless, it is often used with implicit solvents. In 2006, a special version of CHARMM22/CMAP was reparametrized for consistent use with implicit solvent GBSW.