Hi, I have the following question:
Say, I applied an initial velocity on the free end of a cantilever beam, and then released it. I also fixed a temperature of 300 K. The beam keeps vibrating for a very long time. What I want to do is to damp the beam after some time in order to analyze deformation (if there is any). How can I successfully damp the beam so that it will come into rest about its initial position?
Thanks,
That’s not a thermostatting question, nor really an atomistic
question. That motion is macroscopic, for a huge system,
that motion is at the length scale of the entire system, You
would need some dissipative force applied at the scale
of the entire beam, as a function of the beam’s displacement
from its original position. There is nothing like that in LAMMPS,
but I suppose you could write your own fix to apply such a force.
Steve
Thanks you all for the fruitful comments. I will try what Steve suggested to damp the system about its initial configuration. There is one point confusing though. A few comments pointed out that it does not makes sense to use thermostat to mimic the effect of air in the room as a thermostat. A suggestion was to fix only an initial temperature to the system. However, an initial temperature is not conserved with NVE. I guess I still need to employ a thermostat to maintain the system at room temperature.
Thanks you all for the fruitful comments. I will try what Steve suggested to damp the system about its initial configuration. There is one point confusing though. A few comments pointed out that it does not makes sense to use thermostat to mimic the effect of air in the room as a thermostat.
As you can easily find out by putting you hand near an open flame, air is a very bad thermal conductor.
A suggestion was to fix only an initial temperature to the system. However, an initial temperature is not conserved with NVE. I guess I still need to employ a thermostat to maintain the system at room temperature.
Well, there are two issues to consider. First, if you continue from a proper equilibration total energy should be conserved reasonably well. If not, you need to adjust your settings. A thermostat will only hide bad MD settings. Second, the motion of the cantilever will add to the total kinetic energy, but the relative kinetic energy of the cantilever will be conserved. Adding a thermostat will unphysically cool down your system.
…and a need to reiterate, you have to watch your time scales. Forcing your system to be on a different time scale will taint your results.
Axel.