[Pw_forum] some input parameter

Paolo Giannozzi giannozz at democritos.it
Thu Jun 10 13:01:00 CEST 2010

chenjie gu wrote:

> for ion_temperature=andersen: the collision frequency parameter is given 
> as nu=1/tau defined above

"above", in the documentation, you find the following definition:
   tau = nraise*dt. "nraise" is an integer of your choice;
dt is the time step. So the collision frequency parameter nu
of the Andersen thermostat is nu=1/(nraise*dt), or, in a more
transparent way, nu*dt = 1/nraise, that is, every nraise time
steps there is a "collision", i.e. the velocity of one randomly
selected particle gets a random value, distributed according
to the maxwellian distribution for temperature T (I hope I
remember correctly how the Andersen thermostat works).

The way the various thermostats in pw.x are introduced is a
confusing because the same parameter "nraise" has different
meanings for different thermostats.

Paolo Giannozzi, Democritos and University of Udine, Italy

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