About OOPSE OOPSE News Features Download CVS Mailing Lists Documentation Authors Funding Results	The Lennard Jones Force Field The most basic force field implemented in OOPSE is the Lennard-Jones force field, which mimics the van der Waals interaction at long distances and uses an empirical repulsion at short distances. The Lennard-Jones potential is given by: $$V_{\text{LJ}}(r_{ij}) = 4\epsilon_{ij} \biggl[ \biggl(\frac{\sigm... ...j}}{r_{ij}}\biggr)^{12} - \biggl(\frac{\sigma_{ij}}{r_{ij}}\biggr)^{6} \biggr],$$ (3.4) where $r_{ij}$ is the distance between particles $i$ and $j$ , $\sigma_{ij}$ scales the length of the interaction, and $\epsilon_{ij}$ scales the well depth of the potential. Scheme 3.1 gives an example meta-data file that sets up a system of 108 Ar particles to be simulated using the Lennard-Jones force field. Interactions between dissimilar particles requires the generation of cross term parameters for $\sigma$ and $\epsilon$ . These parameters are determined using the Lorentz-Berthelot mixing rules:[12] $$\sigma_{ij} = \frac{1}{2}[\sigma_{ii} + \sigma_{jj}],$$ (3.5) and $$\epsilon_{ij} = \sqrt{\epsilon_{ii} \epsilon_{jj}}.$$ (3.6)
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	Updated on January 16, 2006