<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">Dear Sandro and users,<br><br>Thanks for your clarifications.<br>So, if I want to plot the P-V diagram, I can just calculate the pressure for each volume using the EOS,since the fitting parameters are already known. Is it correct?<br><br>Also, when implementing the fitting procedure iteratively with ev.x, on has to choose between the Murnagham, Birch 1 and Birch 2. According to me, there is nothing in the litterature known as Birch 1 and Birch 2. I thing they refer to Second order and Third order Birch-Murnagham EOS. I would like you to clarify it for me.<br><br><br>Thanks once again<br><br><br><br> ***************************************<br>> Bertrand SITAMTZE YOUMBI<br>> Laboratory of Material Sciences<br>> University of Yaounde I-Cameroon<br>>
*************************************<br><br><br>--- En date de : <b>Mar 2.2.10, Sandro Scandolo <i><scandolo@ictp.it></i></b> a écrit :<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>De: Sandro Scandolo <scandolo@ictp.it><br>Objet: Re: [Pw_forum] Fw : ev.x procedures<br>À: "PWSCF Forum" <pw_forum@pwscf.org><br>Date: Mardi 2 Février 2010, 16h19<br><br><div class="plainMail">Dear Bertrand,<br><br>pressure is not an input of your pw calculation. It is an output of the <br>ev.x calculation.<br><br>What ev.x does is to fit the results of your E(V) pw calculations to a <br>chosen EOS functional form, with a number of parameters. Most functional <br>forms (e.g. Birch-Murnaghan) include the parameters K and K' (see <br><a href="http://en.wikipedia.org/wiki/Birch-Murnaghan_equation_of_state"
target="_blank">http://en.wikipedia.org/wiki/Birch-Murnaghan_equation_of_state</a> ). P(V) <br>can then be calculated from the chosen E(V) (and the fitted parameters) <br>as P(V)=-dE(V)/dV .<br><br>Notice that the P(V) calculated form the EOS with the fitted parameters <br>may be slightly different with respect to the one calculated by pw.x at <br>the volumes where you did your pw.x calculations. But this is another <br>story (related to <br><a href="http://www.quantum-espresso.org/wiki/index.php/Methodological_Background#Stress" target="_blank">http://www.quantum-espresso.org/wiki/index.php/Methodological_Background#Stress</a> <br>).<br><br>So, coming to your question, K' is not obtained by finite differences, <br>but rather directly as a result of the E(V) fit.<br><br>Sandro<br><br><br>Bertrand SITAMTZE wrote:<br>><br>><br>> --- En date de : *Mar 2.2.10, Bertrand SITAMTZE /<<a ymailto="mailto:siyouber@yahoo.fr"
href="/mc/compose?to=siyouber@yahoo.fr">siyouber@yahoo.fr</a>>/* <br>> a écrit :<br>><br>><br>> De: Bertrand SITAMTZE <<a ymailto="mailto:siyouber@yahoo.fr" href="/mc/compose?to=siyouber@yahoo.fr">siyouber@yahoo.fr</a>><br>> Objet: ev.x procedures<br>> À: "pw code" <<a ymailto="mailto:pw_forum@pwscf.org" href="/mc/compose?to=pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br>> Date: Mardi 2 Février 2010, 11h04<br>><br>> (SORRY, THERE WAS A SMALL MISTAKE IN MY PREVIOUS MESSAGE)<br>><br>><br>> Dear all,<br>><br>> As I know, scf and nscf in pw.x are with zero pressure (please<br>> correct me if I am wrong). Thus, when evaluating the EOS<br>> parameters with ev.x, the code uses the E
vs VOLUME data to<br>> evaluate the bulk modulus throught the second derivative. But, how<br>> does the code proceed in order to evaluate the pressure derivative<br>> of the bulk modulus K', without varing the pressure? If otherwise,<br>> can somebody tell me the range of pressure used to evaluate K'?<br>><br>> Please, note that K' is defined as K'=(dK/dP) at P=0.<br>><br>><br>> Thanks very much for your answers.<br>><br>><br>><br>> ***************************************<br>> Bertrand SITAMTZE YOUMBI<br>> Laboratory of Material Sciences<br>> University of Yaounde I-Cameroon<br>>
*************************************<br>><br>><br>><br>> ------------------------------------------------------------------------<br>><br>> _______________________________________________<br>> Pw_forum mailing list<br>> <a ymailto="mailto:Pw_forum@pwscf.org" href="/mc/compose?to=Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>> <a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>> <br><br>-- <br>Sandro Scandolo, ICTP | <a href="http://www.ictp.it/%7Escandolo" target="_blank">http://www.ictp.it/~scandolo</a><br><br>_______________________________________________<br>Pw_forum mailing list<br><a ymailto="mailto:Pw_forum@pwscf.org" href="/mc/compose?to=Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br><a href="http://www.democritos.it/mailman/listinfo/pw_forum"
target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br></div></blockquote></td></tr></table><br>