Hi,
Firstly, you are not constraining (runtype=constraint), but using a harmonic
umbrella potential.
Secondly, your distance of 28.9 nm seems enormous, maybe you mixed
up nanometers and Angstroms here?
Thirdly, I would strongly suggest to switch to Gromacs 4.0.5.
I have completely rewritten the pull code for Gromacs 4
and things now work much easier and better.
Berk
> Date: Mon, 31 Aug 2009 12:18:06 -0500
> From: [email protected]
> To: [email protected]
> Subject: [gmx-users] PMF using umbrella sampling
>
> Hello everyone,
> I'm trying to compute the PMF for pulling two proteins apart. I'm
> planning on setting up several runs where the COM separation of the
> proteins is constrained and the constraint force is measured over the
> course of a long simulation. However, I'm having trouble doing this
> because I'm unsure of the inputs in the .ppa file. I'm trying to do
> this with Gromacs 3.3.3. Here is the .ppa file I'm using:
>
> runtype = umbrella
> ngroups = 1
> reference_group = knob
> reftype = com
> pulldim = Y Y Y
> group_1 = car
> k1 = 1000
> pos1 = 0.0 0.0 28.8989219666
>
> Here, there are two proteins: car and knob. The COM of car is located
> at (0.0 0.0 28.8989219666) relative to knob. The problem I'm
> experiencing is that the simulation results in the two proteins being
> pulled apart instead of constrained at distance pos1. I believe that
> I'm misinterpreting the inputs. Does anyone know the solution?
> Thanks,
> Bob
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