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lammps/doc/fix_temp_rescale.txt
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fix_temp_rescale.txt
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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
fix temp/rescale command :h3
[Syntax:]
fix ID group-ID temp/rescale N Tstart Tstop window fraction keyword values ... :pre
ID, group-ID are documented in "fix"_fix.html command
temp/rescale = style name of this fix command
N = perform rescaling every N steps
Tstart,Tstop = desired temperature at start/end of run (temperature units)
window = only rescale if temperature is outside this window (temperature units)
fraction = rescale to target temperature by this fraction
zero or more keyword/value pairs may be appended
keyword = {region} or {partial} :ul
{region} values = region-ID
region-ID = ID of region to apply rescaling to
{partial} values = xflag yflag zflag
xflag,yflag,zflag = 0/1 if the velocity component should not or should be rescaled :pre
[Examples:]
fix 3 flow temp/rescale 100 1.0 1.1 0.02 0.5
fix 3 boundary temp/rescale 1 1.0 1.5 0.05 1.0 region edge
fix 3 boundary temp/rescale 1 1.0 1.5 0.05 1.0 partial 0 1 1 :pre
[Description:]
Reset the temperature of a group of atoms by explicitly rescaling
their velocities.
Rescaling is performed every N timesteps. The target temperature is a
ramped value between the {Tstart} and {Tstop} temperatures at the
beginning and end of the run.
Rescaling is only performed if the difference between the current and
desired temperatures is greater than the {window} value. The amount
of rescaling that is applied is a {fraction} (from 0.0 to 1.0) of the
difference between the actual and desired temperature. E.g. if
{fraction} = 1.0, the temperature is reset to exactly the desired
value.
The keyword {region} applies the fix only to atoms that are in the
specified geometric region (and in the fix group). Since atoms can
enter/leave a region, this test is performed each timestep.
The keyword {partial} rescales only the specified velocity components.
A compute of style temp/partial is used to compute the current
temperature of just those components (see below).
The {region} and {partial} keywords cannot currently be used together.
A temp/rescale fix does not update the coordinates of its atoms. It
is normally used with a fix of style {nve} that does that. A
temp/rescale fix should not normally be used on atoms that also have
their temperature controlled by another fix - e.g. a
"nvt"_fix_nvt.html or "langevin"_fix_langevin.html fix.
This fix computes a temperature each timestep. To do this, the fix
creates its own compute of style "temp" or "temp/region" or
"temp/partial", as if one of these commands had been issued:
compute fix-ID_temp group-ID temp
compute fix-ID_temp group-ID temp/region region-ID
compute fix-ID_temp group-ID temp/partial xflag yflag zflag :pre
Which is used depends on whether the {region} or {partial} keywords
were specified with the fix. See the "compute
temp"_compute_temp.html, "compute
temp/region"_compute_temp_region.html, and "compute
temp/partial"_compute_temp_partial.html commands for details. Note
that the ID of the new compute is the fix-ID + underscore + "temp",
and the group for the new compute is the same as the fix group.
Note that this is NOT the compute used by thermodynamic output (see
the "thermo_style"_thermo_style.html command) with ID = {thermo_temp}.
This means you can change the attributes of this fix's temperature
(e.g. its degrees-of-freedom) via the
"compute_modify"_compute_modify.html command or print this temperature
during thermodynamic output via the "thermo_style
custom"_thermo_style.html command using the appropriate compute-ID.
It also means that changing attributes of {thermo_temp} will have no
effect on this fix.
[Restart, fix_modify, output, run start/stop, minimize info:]
No information about this fix is written to "binary restart
files"_restart.html.
The "fix_modify"_fix_modify.html {temp} option is supported by this
fix. You can use it to assign a "compute"_compute.html you have
defined to this fix which will be used in its thermostatting
procedure. For consistency, if using the keyword {region}, the
compute you assign should also be of style
"temp/region"_compute_temp_region.html.
The "fix_modify"_fix_modify.html {energy} option is supported by this
fix to add the energy change implied by a velocity rescaling to the
system's potential energy as part of "thermodynamic
output"_thermo_style.html. Note that because this fix is invoked
every N steps and thermodynamic info is printed every M steps, that
unless M is a multiple of N, the energy contribution will be zero.
The potential energy change due to this fix is stored as a scalar
quantity, which can be accessed by various "output
commands"_Section_howto.html#4_15. The scalar value calculated by
this fix is "extensive", meaning it scales with the number of atoms in
the simulation.
The energy change can be printed as part of thermodynamic output via
the keyword f_ID, where ID is the fix-ID of this fix. See the
"thermo_style custom"_thermo_style.html command for details.
This fix can ramp its target temperature over multiple runs, using the
{start} and {stop} keywords of the "run"_run.html command. See the
"run"_run.html command for details of how to do this.
This fix is not invoked during "energy minimization"_minimize.html.
[Restrictions:] none
[Related commands:]
"fix langevin"_fix_langevin.html, "fix nvt"_fix_nvt.html,
"fix_modify"_fix_modify.html
[Default:] none
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