Syntax:
fix ID temp/global/rescale N Tstart Tstop fraction
Examples:
fix 1 temp/global/rescale 100 300.0 300.0 0.5 fix 5 temp/global/rescale 10 300.0 10.0 1.0
Description:
Reset the temperature of all the particles in the entire simulation by explicitly rescaling their velocities. This is a simple thermostatting operation to keep the temperature of the gas near the desired target temperature. This can be useful if an external driving force is adding energy to the system. Or if you wish the heat or cool the temperature of the system over time.
The rescaling is applied to only the translational degrees of freedom for the particles. Their rotational or vibrational degrees of freedom are not altered.
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.
From the current global temperature and the current target temperature, a velocity scale factor is calculated. The amount of rescaling that is applied is adjusted by the fraction parameter which is a value from 0.0 to 1.0. difference between the actual and desired temperature. If fraction = 1.0, the temperature is reset to exactly the desired value. If fraction = 0.5, the temperature is reset to a value halfway between the current global and target temperatures.
The rescaling factor is applied to each of the components of the translational velocity for every particle in the simulation.
Note that this fix performs thermostatting using the same formula for temperature as calculated by the compute temp command. It does not currently subtract out a net streaming velocity to measure a thermal temperature since it assumes the net center of mass velocity for the entire system is zero. An option for this may be added in the future. See the fix temp/rescale doc page for a command that thermostats the thermal temperature on a per-grid-cell basis.
Restart, output info:
No information about this fix is written to binary restart files.
This fix produces no output.
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.
Restrictions: none
Related commands:
Default: none