ISISNeutronMuon / ISISNeutronMuon/MDMC

Does MDMC OPLS-aa force field follow OPLS-aa properly for the lj/coul interaction when lammps engine is used?

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Description

**Description of the error**
In MDMC, there is the option to load the OPLS-aa force field. According to https://pubs.acs.org/doi/10.1021/ja9621760, non-bonded interactions are only applied between atoms separated by three or more bonds, and only 1/2 the interaction strength when separated by three bonds

https://pubs.acs.org/doi/10.1021/ja9621760
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In LAMMPS, you'd need to use the https://docs.lammps.org/special_bonds.html option to do this. It is not clear to me that this is being used in the MDMC code via pylammps.

Default for special bonds is "All 3 Lennard-Jones and 3 Coulombic weighting coefficients = 0.0, angle = no, dihedral = no.". To use OPLS correctly, we need something like `special_bonds lj/coul 0.0 0.0 0.5`, not the default.

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