[gmx-users] Rigid water constraint forces in trajectory output

[Mark Abraham]

Hi,

The trajectory forces do not include the constraint forces. You can verify
that by comparing them with those from mdrun -rerun from 2019.x, because
constraints are not applied in a rerun.

Mark

On Wed, 11 Dec 2019 at 17:39, Jacob Monroe <jimonroe at umail.ucsb.edu> wrote:

> Hi all,
>
> I'm working on calculating radial distribution functions for rigid water
> models using force-sampling methods, so I need to know forces on each atom.
> When outputting the forces for a simulation trajectory, does GROMACS
> include constraint forces? In other words, are the printed forces on each
> atom only the derivative of the potential energy? Or do they also include
> the force necessary to maintain rigidity of the water molecule? If the
> constraint forces are not included, I believe I can calculate them if I
> have the forces and velocities and figure out what the rigid body dynamics
> should be given the force on each particle. Any thoughts would be very much
> appreciated.
>
> Thanks,
> Jacob
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