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Hi, I created the 'ParmEd structure' instance from 'openMM system' and after that, I saved the amber parameter file and coordinate file from the ParmEd structure because I want to use Amber.
But when I am calculating the system's potential energy in Amber, I am getting it different from what I got using openMM. What could be the possible reason for this?
Thanks.

Is this a question about OpenMM or ParmEd? If the latter, I can't help with that.

If it's a question about OpenMM, can you show your code? If possible, give a complete test case that can be used to reproduce the problem, including all input files.

Sorry, I think it is a conversion issue because I have noticed some unusual zeroes in the dihedral force constants in the amber .prmtop file.
Thank you,