[gmx-users] position restraints

[Erik Lindahl]

T. Zaraiskaya wrote:
> How to fix the positions of selected atoms during the simulation run
> in GROMACS?
> 

Use freeze groups; it should be explained somewhere in the manual. It's
easy to create groups with the make_ndx program (or manually). Assuming
you want to freeze 'grp1' completely, and 'grp2' in the x and y 
directions, you can use these options in the mdp file:


freezegrps               = grp1 grp2
freezedim                = y y y y y n

The freezedim option has three fields (y or n) for each group, 
designating whether x,y & z degrees of freedom should be frozen.

Cheers,

Erik