Discrepancies between potentials when using md.charge.pppm

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Sahar

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Feb 16, 2021, 8:31:34 PMFeb 16
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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
8PS180_1.28eps_0.99sig.py
8PS180_1.28eps_0.99sig.log
8PS180.xml

Joshua Anderson

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Feb 18, 2021, 6:46:59 AMFeb 18
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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.
------
Joshua A. Anderson, Ph.D.
Research Area Specialist, Chemical Engineering, University of Michigan
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> <8PS180_1.28eps_0.99sig.py><8PS180_1.28eps_0.99sig.log><8PS180.xml>

Joshua Anderson

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Jul 26, 2021, 3:32:31 PMJul 26
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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.
------
Joshua A. Anderson, Ph.D.
Research Area Specialist, Chemical Engineering, University of Michigan

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