[lammps-users] non equilibrium MD

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1

Hello,

I have two questions regarding non equilibrium MD (with external force) simulations in LAMMPS.

  1. If we use a thermostat (with T=300 K), will it subtract the non zero streaming velocity to maintain the temperature or will it reset the total velocity.
  2. How do we remove the COM motion only due to thermal noise and keep the motion due to the external force as it is.

Thanks.

Sincerely
Apoorv

2

Hello,

1) If we use a thermostat (with T=300 K), will it subtract the non zero
streaming velocity to maintain the temperature

Only if you ask lammps to, see:
http://lammps.sandia.gov/doc/Section_howto.html#4_16

More precisely, if you expect the system to move as a block (plug
flow), then you can simply remove the center of mass velocity using
fix_modify and compute temp/com.

For a more complex flow, one can use compute temp/profile, or more
simply only apply the thermostat in the directions perpendicular to
the applied force with compute temp/partial.

2) How do we remove the COM motion only due to thermal noise and keep the
motion due to the external force as it is.

By averaging it.

Best,
Laurent