[Pw_forum] variable cell MD target pressure

[luisen]

  Dear all,

  I am writing to ask for confirmation about a "strange" feature in
  the program, that concerns molecular dynamics calculations at finite
  temperature (non-zero) with variable cell.
  As far as I have experienced it seems to me that the target pressure
  that one states in the input file is the total pressure, I mean, including
  the kinetic term coming from the motion of the ions due to the temperature,
  while the stress tensor and pressure writen in the output file includes only
  the potential terms, but not the kinetic ones.

  This message is just to request a confirmation from the developers that I am
  correct about this.

  Note that this feature is very confusing for users; I could spot it because
  the system I am studying is liquid Be, which has a very high temperature and
  a very high number density, so that the kinetic part of the pressure is 20
  kbar. So it is really confusing asking for 0 kbar and obtaining
  oscillations around -20 kbar in the output file.
  May I suggest to modify it in the future release of QE?

  Yours,
  	Luis Enrique Gonzalez
  	Universidad de Valladolid