OPLS force fields functional form

The non polarizable OPLS force fields can be written by using the following functional form (Jorgensen et al., 1996). 

Hach molecular mechanics method has its own functional form MM+. AMBER, OPL.S, and BIO+. The functional form describes the an alytic form of each of th e term s in th e poteri tial. For exam pie, MM+h as both a quadratic and a cubic stretch term in th e poten tial whereas AMBER, OPES, and BIO+ have only c nadratic stretch term s, I h e functional form is referred to here as the force field. For exam pie, th e fun ction al form of a qu adratic stretch with force constant K, and equilibrium distance i q is ... 

The CLAP model was built based on the OPLS-AA force field [21] functional form which means that, technically, it is easy to combine any molecule or residue already defined in the OPLS-AA database with the structures developed for ionic... 

Force fields for [BMIM][PF6] that explicitly treat aU hydrogens (all-atom models) were developed soon after this by Margulis et al. [14], and Morrow and Maginn [11], while Stassen and coworkers [83] published a force field for the [EMIM]+ and [BMIM]+ cations paired with tetrachloroaluminate and tetrafluoroborate anions. The force fields aU have similar functional forms, and parameters were again maiiily developed using literature force field parameters for similar compounds and ab initio calculations of single ions or ion pairs. In these and later studies, repulsion-dispersion parameters were generally adapted from those available from one of three popular force field databases (Amber [114], OPLS [118] and CHARMM [119]). For [BMIM][PF6], the added realism of the all-atom model enabled densities to be predicted vyithin 1% of the experimental value [11]. The first indications of restricted dynamics in these systems were also observed [11,14,15]. 

The most common approach to develop a classieal foree field for an ionie liquid is to represent the bonding and energetics with simplified analytical potential functions, which are inexpensive to evaluate numerically. Such a force field is typically based on an OPLS-AA/AMBER framework with two types of torsions (proper and improper) and has the following form for the total potential energy... 

---