[gmx-users] free energy with TIP4P bug fixed

[Berk Hess]

Hi,

Sorry for not being clear on this issue.
I am currently following and preparing lectures and exercises for a workshop
and do not have time to sit back and go deeply into this issue.

What my conclusion is from looking at the code:
With TIP4P water and free-energy any non-perturbed atoms
that are in the same energy group as perturbed atoms might
have missing Coulomb interactions with TIP4P.

Thus the only simulations TIP4P free-energy simulations that are surely correct are:
Have a separate energy group that contains only perturbed particles,
possible combined with non-perturbed particles that have no charge.
Or using the environment variable GMX_NO_SOLV_OPT.

The bug actually also affects another situation:
TIP4P and free-energy combined with rcoulomb > rvdw could lead to missing
Coulomb interactions beyond rvdw between TIP4P and charges in the same
energy group as perturbed particles.
But this probably nobody has tried.

Berk


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