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