[gmx-users] ramping force constants

Mark Abraham Mark.Abraham at anu.edu.au
Thu Mar 6 00:20:56 CET 2008

D. Flemming Hansen wrote:
> Dear All,
> I was wondering if there is a way to ramp (gradually change) a force 
> constant during a simulation? For example, I introduce some distance 
> restraints in my simulation, and I would like the force constant to be 
> very small initially (to prevent the calculation from crashing), and 
> slowly increase the force constant during the simulation - is there an 
> easy way of doing so?
> The only way I found to do this is to run a series of simulations - 
> simply changing the disre_fc parameter in each step.

Unless you can manage to hijack the free-energy perturbation code, this 
is the only way you can do it. It's straightforward to write a series of 
.mdp files and a job script with alternating calls to grompp and mdrun, 
however. The file I/O cost will be much higher than a normal run, but I 
imagine you're not planning too many such runs.


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