[gmx-users] Flat-bottomed position restraint set

Justin Lemkul jalemkul at vt.edu
Wed Nov 12 14:55:10 CET 2014

On 11/12/14 8:08 AM, liuyong_1007 at dicp.ac.cn wrote:
> Dear Gromacs users!
> I use the flat-bottomed position restraints to avoid the molecules to escape from the clusters to the vacuum. The parameters of the restraints on water molecules are shown as follow:
> ; Position restraint for each water oxygen
> [ position_restraints ]
> ;  i   funct       g         r(nm)       k
>     1    2        1          3         30.0
>     2    2        1          3         30.0
>     3    2        1          3         30.0
> #endif
> However, water molecules still escape away from the cluster to the vacuum after about 100 ns MD run at 550K. What should be done with the restraints to avoid the water molecules to escape to the vacuum?

Are you using suitable reference coordinates passed to grompp -r?  If you're 
not, then the reference coordinates are whatever is in grompp -c, which means 
your water molecules can deviate up to 3 nm from that position without penalty. 
  For a sphere, the reference coordinates for the water should be the geometric 
center of the sphere.



Justin A. Lemkul, Ph.D.
Ruth L. Kirschstein NRSA Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 629
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

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


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