[gmx-developers] Zero short-range energy of TIP3P

[Igor Leontyev]

Dear gmx developers,
The short range energy terms (Coul and VdW) for a single water molecule in the bulk (rigid TIP3P) simulated with gmx-2020 and extracted from edr-file are exact zero. The result looks strange to me. The same but with gmx-5.1 gives non-zero (presumably correct) interaction energy of water.

How I do it:
1. Generate an index file with indices of the specific water molecule in the bulk (e.g. for the 1st H2O it is just 1 2 3) to be monitored.
2. Specify the energy group of the molecule to be monitored in mdp file and run MD.
3. After MD, use gmx energy to get LJ and Coulomb (SR) interactions of the energy group from the edr file.
The computed with gmx-2020 non-bonded (SR) energies of this energy group are zero.

Please, let me know if I am doing something wrong. Otherwise, it looks like a bug because old version (gmx-5.1) results in non-zero energies that looks reasonable.

Thanks,
Igor
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