"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

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:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

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fix spring/self command :h3

[Syntax:]

fix ID group-ID spring/self K :pre

ID, group-ID are documented in "fix"_fix.html command
spring/self = style name of this fix command
K = spring constant (force/distance units) :ul

[Examples:]

fix tether boundary-atoms spring/self 10.0 :pre

[Description:]

Apply a spring force independently to each atom in the group to tether
it to its initial position.  The initial position for each atom is its
location at the time the fix command was issued.  At each timestep,
the magnitude of the force on each atom is -Kr, where r is the
displacement of the atom from its current position to its initial
position.

[Restart, fix_modify, output, run start/stop, minimize info:]

This fix writes the original coordinates of tethered atoms to "binary
restart files"_restart.html, so that the spring effect will be the
same in a restarted simulation.  See the
"read_restart"_read_restart.html command for info on how to re-specify
a fix in an input script that reads a restart file, so that the
operation of the fix continues in an uninterrupted fashion.

The "fix_modify"_fix_modify.html {energy} option is supported by this
fix to add the energy stored in the per-atom springs to the system's
potential energy as part of "thermodynamic output"_thermo_style.html.

This fix computes a scalar energy which can be accessed by various
"output commands"_Section_howto.html#4_15.  This energy is the sum of
the spring energy for each atom, where the per-atom energy is 0.5 * K
* r^2.

No parameter of this fix can be used with the {start/stop} keywords of
the "run"_run.html command.

The forces due to this fix are imposed during an energy minimization,
invoked by the "minimize"_minimize.html command.

IMPORTANT NOTE: If you want the per-atom spring energy to be included
in the total potential energy of the system (the quantity being
minimized), you MUST enable the "fix_modify"_fix_modify.html {energy}
option for this fix.

[Restrictions:] none

[Related commands:]

"fix drag"_fix_drag.html, "fix spring"_fix_spring.html, 
"fix smd"_fix_smd.html, "fix spring/rg"_fix_spring_rg.html

[Default:] none
