fix ID group-ID temp/rescale N Tstart Tstop window fraction
Tstart can be a variable (see below)
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 fix 3 boundary temp/rescale 1 1.0 1.5 0.05 1.0
Reset the temperature of a group of atoms by explicitly rescaling their velocities.
The rescaling is applied to only the translational degrees of freedom for the particles, which is an important consideration if finite-size particles which have rotational degrees of freedom are being thermostatted with this fix. The translational degrees of freedom can also have a bias velocity removed from them before thermostatting takes place; see the description below.
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.
Tstart can be specified as an equal-style variable. In this case, the Tstop setting is ignored. If the value is a variable, it should be specified as v_name, where name is the variable name. In this case, the variable will be evaluated each timestep, and its value used to determine the target temperature.
Equal-style variables can specify formulas with various mathematical functions, and include thermo_style command keywords for the simulation box parameters and timestep and elapsed time. Thus it is easy to specify a time-dependent temperature.
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.
IMPORTANT NOTE: Unlike the fix nvt command which performs Nose/Hoover thermostatting AND time integration, this fix does NOT perform time integration. It only modifies velocities to effect thermostatting. Thus you must use a separate time integration fix, like fix nve to actually update the positions of atoms using the modified velocities. Likewise, this fix should not normally be used on atoms that also have their temperature controlled by another fix - e.g. by fix nvt or fix langevin commands.
See this howto section of the manual for a discussion of different ways to compute temperature and perform thermostatting.
This fix computes a temperature each timestep. To do this, the fix creates its own compute of style "temp", as if one of this command had been issued:
compute fix-ID_temp group-ID temp
See the compute temp 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 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 command or print this temperature during thermodynamic output via the thermo_style custom command using the appropriate compute-ID. It also means that changing attributes of thermo_temp will have no effect on this fix.
Like other fixes that perform thermostatting, this fix can be used with compute commands that calculate a temperature after removing a "bias" from the atom velocities. E.g. removing the center-of-mass velocity from a group of atoms or only calculating temperature on the x-component of velocity or only calculating temperature for atoms in a geometric region. This is not done by default, but only if the fix_modify command is used to assign a temperature compute to this fix that includes such a bias term. See the doc pages for individual compute commands to determine which ones include a bias. In this case, the thermostat works in the following manner: the current temperature is calculated taking the bias into account, bias is removed from each atom, thermostatting is performed on the remaining thermal degrees of freedom, and the bias is added back in.
Styles with a cuda suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed in Section_accelerate of the manual. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues.
These accelerated styles are part of the USER-CUDA package. They are only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.
You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the -suffix command-line switch when you invoke LAMMPS, or you can use the suffix command in your input script.
See Section_accelerate of the manual for more instructions on how to use the accelerated styles effectively.
Restart, fix_modify, output, run start/stop, minimize info:
No information about this fix is written to binary restart files.
The fix_modify temp option is supported by this fix. You can use it to assign a temperature compute you have defined to this fix which will be used in its thermostatting procedure, as described above. For consistency, the group used by this fix and by the compute should be the same.
The fix_modify 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.
This fix computes a global scalar which can be accessed by various output commands. The scalar is the cummulative energy change due to this fix. The scalar value calculated by this fix is "extensive".
This fix can ramp its target temperature over multiple runs, using the start and stop keywords of the run command. See the run command for details of how to do this.
This fix is not invoked during energy minimization.
fix langevin, fix nvt, fix_modify