[gmx-developers] Recalculating forces every N steps

Berk Hess hess at kth.se
Wed Feb 5 14:40:13 CET 2014

On 02/05/2014 02:26 PM, Szilárd Páll wrote:
> You should be able to use the force flags, I think. These encode what
> needs to be done every step (e.g. NS step or not, energy or
> force-only), it gets set in do_md and passed to do_force.
That's only the easy part.
Then you need to use a multiple timestep integrator. We have such an 
integrator, but it's currently linked to twin-range non-bonded 
interactions. You would need to modify some control code to make it work 
on your potential. The essential function is combine_forces in 
mdlib/update.c which combines the fast and slow forces for the integrator.


> Cheers,
> --
> Szilárd
> On Wed, Feb 5, 2014 at 12:51 PM, Alexander Björling
> <alex.bjorling at gmail.com> wrote:
>> Hi,
>> Our new bonded interaction (at https://gerrit.gromacs.org/#/c/2659/) is very
>> expensive to evaluate and gives rise to a force which varies slowly in time.
>> I'd like these forces to only be updated every N steps and to remain
>> constant in between. What is the proper way to achieve this?
>> Best,
>> Alex
>> --
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