OPLS force field

The optimized potentials for liquid simulations (OPLS) force-field was developed for the simulation of proteins and other organic liquids.

OPLS-all atom

(OPLS-AA)

Form of the force field

Bond stretching

$E_{\rm {bond}}=\sum _{\rm {bonds}}K_{r}\left(r-r_{eq}\right)^{2}$

Angle bending

$E_{\rm {angle}}=\sum _{\rm {angles}}K_{\theta }\left(\theta -\theta _{eq}\right)^{2}$

Torsion

$E(\phi )={\frac {V_{1}}{2}}\left[1+\cos(\phi +f1)\right]+{\frac {V_{2}}{2}}\left[1-\cos(2\phi +f2)\right]+{\frac {V_{3}}{2}}\left[1+\cos(3\phi +f3)\right]$

Non-bonded

$E_{ab}=\sum _{i}^{\rm {on~a}}\sum _{j}^{\rm {on~b}}\left[{\frac {q_{i}q_{j}e^{2}}{r_{ij}}}+4\epsilon _{ij}\left({\frac {\sigma _{ij}^{12}}{r_{ij}^{12}}}-{\frac {\sigma _{ij}^{6}}{r_{ij}^{6}}}\right)\right]f_{ij},~~~~f_{ij}=\left\{{\begin{array}{lll}0.5&;&{\rm {if}}~~i,j=1,4\\1&;&{\rm {otherwise}}\end{array}}\right.$