[Pw_forum] Temperature extraction from PW

[Zahraa Ibrahim]

Hello PWSCF users

I recently changed from the democritus version of PW to the espresso version.
I noticed that the temperature in the espresso version is calculated from 
T = 2 * (kinetic energy - center of mass energy) / (3N-3) [I am not setting any constraints] while in the democritus version it was calculated by dividing the numerator by (3N).  (N being the number of particles).
I was wondering what exactly this extra 3 stands for.

Another, probably related, question is about the effect of periodic boundary conditions on the temperature. I am simulating thermal motion in a solid with a relatively small number of atoms. Do the periodic boundary conditions change the degrees of freedom of the solid in any ways, that need to be taken into account in the temperature estimation.  

Greetings
Zahraa Ibrahim

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