[gmx-users] the difference between fixing and freezing and position restraint

Justin A. Lemkul jalemkul at vt.edu
Sat Jan 28 15:30:50 CET 2012

Banafsheh Mehrazma wrote:
> Hi everyone;
> I wonder what's the difference between fixing and freezing and
> position restraining?
> I know how to position restrain, but I don't have any idea how we can
> fix or freeze.
> So I would be glad if you tell me exactly, how we can fix the solute
> while the solvent is not, and vice versa. :)

Freezing is done via freezegrps (and related settings) in the .mdp file.  The 
positions of the frozen atoms are invariant.

Restraining simply applies a biasing potential to the atoms such that 
displacement is disfavored.  The strength of the restraint is controlled by the 
force constant in the posre.itp file.



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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