答复: [gmx-users] error in umbralla sampling step 6

[Justin Lemkul]

Please keep the discussion on the list.

On 10/27/13 5:09 AM, sunyeping wrote:
> Dear professor Lemkul,
>
> For warning 1:
> I use the npt_umbrella.mdp file you provided in step 6 in the umbralla sampling
> tutorial. You told us to start by running a brief NPT equilibration in each
> window using this mdp file. If Parrinello-Rahman pressure coupling should be
> used, why did you put it in the mdp file?
>

I know the tutorial system is robust enough that it won't matter.  That is not 
necessarily true for whatever other system you come up with.  Be careful when 
extrapolating something that works in a tutorial with something that is 
untested.  The general logic is the same (you need to equilibrate for a little 
while first), but you have to think a bit about the proper settings.  There is 
also no guarantee that the length of time I set in the tutorial simulation 
processes (equilibration, SMD, and umbrella sampling) will necessarily be 
sufficient for whatever you're doing.

> For warning 2:
> I check the gro files using vmd but I cann't find any molecule broken? How can I
> find the brroken molecule?

The only way to find them is to look.  I have no special advice for this.

> I add -pbc whole option to the  trjconv as following:
>
> trjconv -s pull.tpr -f traj.xtc -o conf.gro -sep -pbc whole
>
> then It seems that the problemis solved. Is that a correct wayyou mean to solve the problem?
>

Then clearly something was broken across PBC, which means there is no real problem.

-Justin

-- 
==================================================

Justin A. Lemkul, Ph.D.
Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 601
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

jalemkul at outerbanks.umaryland.edu | (410) 706-7441

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