forked from lijiext/lammps
67 lines
2.3 KiB
Plaintext
67 lines
2.3 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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fix spring/rg command :h3
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[Syntax:]
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fix ID group-ID spring/rg K RG0 :pre
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ID, group-ID are documented in "fix"_fix.html command
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spring/rg = style name of this fix command
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K = harmonic force constant (force/distance units)
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RG0 = target radius of gyration to constrain to (distance units) :ul
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if RG0 = NULL, use the current RG as the target value :pre
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[Examples:]
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fix 1 protein spring/rg 5.0 10.0
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fix 2 micelle spring/rg 5.0 NULL :pre
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[Description:]
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Apply a harmonic restraining force to atoms in the group to affect
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their central moment about the center of mass (radius of gyration).
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This fix is useful to encourage a protein or polymer to fold/unfold
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and also when sampling along the radius of gyration as a reaction
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coordinate (i.e. for protein folding).
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The radius of gyration is defined as RG in the first formula. The
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energy of the constraint and associated force on each atom is given by
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the second and third formulas, when the group is at a different RG
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than the target value RG0.
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:c,image(Eqs/fix_spring_rg.jpg)
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The (xi - center-of-mass) term is computed taking into account
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periodic boundary conditions, m_i is the mass of the atom, and M is
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the mass of the entire group. Note that K is thus a force constant
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for the aggregate force on the group of atoms, not a per-atom force.
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If RG0 is specified as NULL, then the RG of the group is computed at
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the time the fix is specified, and that value is used as the target.
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[Restart, fix_modify, output, run start/stop, minimize info:]
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No information about this fix is written to "binary restart
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files"_restart.html. None of the "fix_modify"_fix_modify.html options
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are relevant to this fix. No global or per-atom quantities are stored
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by this fix for access by various "output
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commands"_Section_howto.html#howto_15. No parameter of this fix can
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be used with the {start/stop} keywords of the "run"_run.html command.
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This fix is not invoked during "energy minimization"_minimize.html.
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[Restrictions:] none
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[Related commands:]
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"fix spring"_fix_spring.html, "fix spring/self"_fix_spring_self.html
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"fix drag"_fix_drag.html, "fix smd"_fix_smd.html
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[Default:] none
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