CHARMM (Wikipedia)
CHARMM force field (see also CGenFF)
K Vanommeslaeghe, E Hatcher, C Acharya, S Kundu, S Zhong, J Shim, E Darian, O Guvench, P Lopes, I Vorobyov, A D Mackerell Jr, CHARMM general force field: A force field for drug-like molecules compatible with the CHARMM all-atom additive biological force fields, JCC 31, 671 (2009)