<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div><span>Thank you Giuseppe<br></span></div><div> </div><div>DEBBICHI Mourad<br>Unité de Recherche Physique des Solides,99/UR/13-19,<br>Département de Physique, Faculté des Science de Monastir,<br>Avenue de l'Environnement 5019, Monastir Tunisie.<br>tél:+21697487042<br>mourad_fsm@yahoo.fr<br></div> <div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"> <div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"> <div dir="ltr"> <font face="Arial" size="2"> <hr size="1"> <b><span style="font-weight: bold;">De :</span></b> Giuseppe Mattioli <giuseppe.mattioli@ism.cnr.it><br> <b><span style="font-weight: bold;">À :</span></b> debbichi mourad <mourad_fsm@yahoo.fr>; PWSCF Forum <pw_forum@pwscf.org> <br> <b><span style="font-weight: bold;">Envoyé
le :</span></b> Mardi 19 juin 2012 12h27<br> <b><span style="font-weight: bold;">Objet :</span></b> Re: [Pw_forum] (no subject)<br> </font> </div> <br><br>Dear Mourad<br>No special keywords, only a bit of physical chemistry...<br>Let us suppose we are calculating The formation heat (aka formation enthalpy, DeltaH_f) of wurtzite <br>ZnO. First of all, what is it the formation enthalpy? Suppose that we are not very rigorous, we may <br>say "the energy gained to form ZnO from Zn and O in their standard state". We may consider therefore <br>this chemical process:<br><br>Zn(metal)+O2(gas)-->ZnO(wurtzite)<br><br>How can we calculate such an energy? Well, all chemical "Delta" quantities are defined as a difference <br>between some final state quantity (free energy, enthalpy, ...) and the related initial state <br>quantity. If we consider negligible the PV contribution to the above chemical process (H = U+PV), we <br>can estimate formation heats as
differences of total energies calculated in supercells:<br><br>DeltaH_f (ZnO) = E(ZnO) - E(Zn) - E(O2)<br><br>You must only be sure that the number of atoms in all the supercells is fully consistent with your <br>calculation:<br><br>ZnO(wurtzite): 4 atoms (2 ZnO units)<br>Zn(metal, hcp): 1 atom<br>O2 molecule: 2 atoms<br><br>Your final equation is therefore<br><br>DeltaH_f (ZnO) = E(ZnO) - 2*E(Zn) - E(O2)<br><br>Modify it according to your purpose...<br><br>HTH<br><br>Giuseppe<br><br><br>On Tuesday 19 June 2012 11:21:54 debbichi mourad wrote:<br>> Dear pwscf users.<br>> How to calculate the formation enthalpy, which command I can added to the<br>> input? best regards<br>> <br>> DEBBICHI Mourad<br>> Unité de Recherche Physique des Solides,99/UR/13-19,<br>> Département de Physique, Faculté des Science de Monastir,<br>> Avenue de l'Environnement 5019, Monastir Tunisie.<br>> tél:+21697487042<br>> <a
ymailto="mailto:mourad_fsm@yahoo.fr" href="mailto:mourad_fsm@yahoo.fr">mourad_fsm@yahoo.fr</a><br><br>-- <br>********************************************************<br>- Article premier - Les hommes naissent et demeurent<br>libres et ègaux en droits. Les distinctions sociales<br>ne peuvent être fondèes que sur l'utilitè commune<br>- Article 2 - Le but de toute association politique<br>est la conservation des droits naturels et <br>imprescriptibles de l'homme. Ces droits sont la libertè,<br>la propriètè, la sùretè et la rèsistance à l'oppression.<br>********************************************************<br><br> Giuseppe Mattioli <br> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA <br> v. Salaria Km 29,300 - C.P. 10 <br> I 00015 - Monterotondo Stazione (RM)
<br> Tel + 39 06 90672836 - Fax +39 06 90672316 <br> E-mail: <<a ymailto="mailto:giuseppe.mattioli@ism.cnr.it" href="mailto:giuseppe.mattioli@ism.cnr.it">giuseppe.mattioli@ism.cnr.it</a>><br><br><br> </div> </div> </div></body></html>