On Mar 25, 2010, at 4:16 PM, Jiayu Dai wrote: > Dear all, > > I found in the previous discussion that the energy in PWscf using Fermi-Dirac > smearing is the free energy.
It is *NOT* any free energy of any physical system. It can be interpreted as the free energy of a system of electrons in the field of clamped nuclei, at the *fictitious* temperature corresponding to the smearing you use. The reason why this concept is useful is that the free energy is variational, while the internal energy is not. That's why Hellman-Feynman forces are derivatives of the free energy, but not of the internal energy. > Is it the total free energy including electrons and ions contribution? As said, electrons only. > Furthermore, how to get the internal energy here? The kinetic energy is easy > to calculate, but how about the potential energy? You do not need any internal energy. what you may actually want to estimate is the T->0 extrapolation of both the free and internal energies (which coincide in the T->0 limit). I think that some estimate of this are available in the pw output, but others may know more than me about this. Stefano B > > Thanks a lot. > > Jiayu > ---------------- > ------------------------------------------- > Jiayu Dai > Department of Physics > National University of Defense Technology, > Changsha, 410073, P R China > ----------------------------------------- > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum --- Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) La morale est une logique de l'action comme la logique est une morale de la pens?e - Jean Piaget Please, if possible, don't send me MS Word or PowerPoint attachments Why? See: http://www.gnu.org/philosophy/no-word-attachments.html -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100325/be582b8b/attachment-0001.htm
