Discrepancies between potentials when using md.charge.pppm

[Sahar]

Hi,

I am running atomistic MD simulations using the OPLS-AA force fields and md.charge.pppm method for long-range electrostatics, but the potential-energy in the log file doesn't match with the sum of all interactions which are bond, angle, dihedral, lj, special lj, special coul, ewald, and pppm energy. So, the potential_energy and sum of all interactions are not equal except for the first timestep and also when pppm is disabled. 

Thanks,

Sahar

[Joshua Anderson]

Sahar,

Thanks for reporting. I have received multiple reports of this behavior. I think it is a bug in the way `potential_energy` and/or the pppm energy is reported to the logger, but I am not certain. I have asked the developer of the code to investigate.
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Joshua A. Anderson, Ph.D.
Research Area Specialist, Chemical Engineering, University of Michigan

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[Joshua Anderson]

Sahar,

This pull request adds PPPM to the v3 API: https://github.com/glotzerlab/hoomd-blue/pull/1066
In it, I added a unit test to ensure that the PPPM energy loggable quantity is reported correctly.

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Joshua A. Anderson, Ph.D.
Research Area Specialist, Chemical Engineering, University of Michigan