[gmx-users] RB dihedral again and dihedral constants

[nanyu101]

Dear Dr.David,
  Thanks for your prompt reply.I have known there are many parameters for RB dihedral type in OPLS.But if I want to simulate my system in ffG43a2 force field, where should I put these force constants that I have already fitted them ourselves.
  By the way,I have met something very interesting when I try to understand how the torsion parameters work. I have done as follows:
1.I have changed all the dihedral force constants to zero and run energy minimization of my system,the Gromacs give me the same results as before I have changed the dihedral force constant. Do you know what has happened?
2.Firstly,I think that Gromacs has not read ffG43a2bond.itp file,so I have change one bond constant to zero,the result changed.Now,we can conclude that Gromacs has read ffG43a2bond.itp file,but why didn't it read the dihedral part?
 Do Gromacs do some special operation when the force constant is zero?
Thanks for your help and any comment is appreciated.

Best wishes,
Xianhui Wu
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