[gmx-developers] solvation free energy with couple-intramol set to 'no'
vgapsys at gwdg.de
Thu Feb 27 14:46:18 CET 2020
I have encountered an unexpected outcome when calculating solvation free
energies and using the option: couple-intramol = no
The observation is that the forces, overall electrostatic energy and the
final free energy depend on the rcoulomb cutoff, in spite of using PME.
I speculate that the following might be happening: for this simulation,
intramolecular interactions are replaced by explicit pair interactions,
however, this apparently is done for both states - coupled and
decoupled. This way, in the coupled state those intramolecular
electrostatic interactions that are outside of the rcoulomb cutoff are
counted twice (when using PME): once they are counted explicitly
ignoring the rcoulomb cutoff, second time they appear in the reciprocal
part of PME.
This can be verified by extending rcoulomb up to the point where all the
intramolecular interactions are within the rcoulomb cutoff. When
extending the cutoff further from that point the overall electrostatic
energy becomes rcoulomb independent.
Such a dependence on rcoulomb is problematic, as tunepme can change
rcoulomb value during runtime.
Let me know if I am overlooking something and maybe this behaviour can
Project Leader at Max Planck Institute for Biophysical Chemistry
Computational biomolecular dynamics group
Am Fassberg 11
D-37077 Goettingen, Germany
Phone: +49 551 201-2310
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