[gmx-users] how to set pull_rate

Justin A. Lemkul jalemkul at vt.edu
Fri Mar 26 02:45:55 CET 2010

Qian Wang wrote:
> Hi,
> I want to use pulling code. But I do not quite sure the meaning of 
> pull_rate. User guide saies this is the rate of change of the reference 
> position. So if I set this value to 0.0001, does it mean the reference 
> postion will move 0.0001 nm/ps ? If yes, how to define the moving 
> direction? Generally speaking, how to choose the value for this 
> parameter? Thanks very much.

The pull_rate parameter is the velocity of the biasing force, in the case of a 
harmonic potential, for instance, this is the velocity at which the spring 
moves, not necessarily the velocity at which the pull group is being moved, 
based on the evolution of the forces.  The pull_vec1 parameter sets the vector 
along which the force is applied.

As for the pull rate, that is a complicated question.  You need to pull fast 
enough to make the simulation feasible, but slow enough such that you do not 
significantly perturb the dynamics, i.e., a sudden, sharp pull that violently 
abstracts your pulled group :)  There is plenty of literature out there with 
regards to pulling.  I'd suggest you do some reading.  You can do some of your 
own testing by using several pull rates and examining the effect the rate has on 
the resulting trajectories.


> Qian


Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080


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