On Oct 15, 2010, at 11:27 AM, meysam pazoki wrote: > > Dear Stefano > > Thanks for your good answer.I am an experimentalist and I learn good new > things from your answer. > My mistake was that I didnt know in calculation of pressure,we neglect > electronic degrres of freedom(I will be thankfull to you,if you introduce a > reference about this subject).
I am sorry to keep correcting you. I don't think I ever said that you can disregard the electronic degrees of freedom when calculating the pressure. I said you can neglect them *in the BO approximation*, when dealing with thermodynamics. I could have been more precise by saying that when doing thermodynamics in the BO approximation, you can safely assume that the "electronic temperature" is zero, i.e. that electrons can be considered in their ground state. In the BO approximations, electrons are kind of slaves who keep atoms together, but do participate in the (thermo) dynamics. The fact that they are slave does imply that you can do without them ... > I have another question :Is these terms are right? > E=-PV+uN+TS => dE=-PdV-VdP+udN+Ndu+Tds+SdT NO - this is nonsense. Nor the energy, nor its differential are what you write. As said in my previous post, the energy is an extensive function of the three extensive quantities S,V,N: E=E(S,V,N) ? -PV+uN+TS. In calculating its differential, you should vary only the variables it depends upon (i.e., S,V,N). > and we know from first law of thermodynamics that dE=-PdV+udN+Tds This is correct, in fact it is different from the expression you gave before. Form this relation you can conclude that P=-?E/?V; T=?E/?S, ?=?E/?N. The first relation is what you need > and we conclude that -VdP+Ndu+SdT=0 NO - see above > and in zero temrature and fixed number of atoms > we have dE=-PdV and P=-dE/dV right, for the wrong reason (i.e. your conclusion is correct, the argument you use to derive it is not) > Thanks You are welcome. You asked a well posed question, and it is a pleasure to answer well posed questions. I think you should study some basic thermodynamics / statistical mechanics. Chandler's book is a very good starting point. Regards - SB --- 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/20101015/b53e3557/attachment.htm
