[gmx-users] forcefield.itp file for gromos45a3 and oplsaa

[XUEMING TANG]

Hello

I am trying to adjust compound LJ parameter in oplsaa (sigma&epsilon) and
also in Gromos (C6 and C12) forcefield for comparison. The original
ffnonbonded.itp file in oplsaa.ff has no pair potential listed. While the
original ffnonbonded.itp file in gromos**.ff listed all the pair
potentials. If I change one atom potential, do I need to do anything to
generate the new pair potential before running a simulation in opls-aa
force field? Or how to generate the pair potentials? While for the case of
gromos forcefield, the forcefield.itp file shows no pair potential will be
generated. Is there any automatic ways to generate the modified LJ
potentials? Should I list every possible LJ pair potentials in
nonbonded.itp file? It looks like some very tedious work if several atoms
are going to be modified.
Also, what does fudge LJ and fudgeQQ mean in forcefield.itp file? Values of
those two are different for OPLS and Gromos.

Thanks in advance and happy new year!
Best!
Xueming
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