fix spring/rg command
Syntax
fix ID group-ID spring/rg K RG0
ID, group-ID are documented in fix command
spring/rg = style name of this fix command
K = harmonic force constant (force/distance units)
RG0 = target radius of gyration to constrain to (distance units)
if RG0 = NULL, use the current RG as the target value
Examples
fix 1 protein spring/rg 5.0 10.0
fix 2 micelle spring/rg 5.0 NULL
Description
Apply a harmonic restraining force to atoms in the group to affect their central moment about the center of mass (radius of gyration). This fix is useful to encourage a protein or polymer to fold/unfold and also when sampling along the radius of gyration as a reaction coordinate (i.e. for protein folding).
The radius of gyration is defined as RG in the first formula. The energy of the constraint and associated force on each atom is given by the second and third formulas, when the group is at a different RG than the target value RG0.
The (
If
Restart, fix_modify, output, run start/stop, minimize info
This fix writes the currently used reference RG (
None of the fix_modify options are relevant to this fix.
This fix computes a global scalar which can be accessed by various
output commands. The scalar is the reference
radius of gyration
No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during energy minimization.
The fix_modify respa option is supported by this fix. This allows to set at which level of the r-RESPA integrator the fix is adding its forces. Default is the outermost level.
Restrictions
This fix is part of the EXTRA-FIX package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.
Default
none