Thank you Giuseppe ? DEBBICHI Mourad Unit? de Recherche Physique des Solides,99/UR/13-19, D?partement de Physique, Facult? des Science de Monastir, Avenue de l'Environnement 5019, Monastir Tunisie. t?l:+21697487042 mourad_fsm at yahoo.fr
________________________________ De?: Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it> ??: debbichi mourad <mourad_fsm at yahoo.fr>; PWSCF Forum <pw_forum at pwscf.org> Envoy? le : Mardi 19 juin 2012 12h27 Objet?: Re: [Pw_forum] (no subject) Dear Mourad No special keywords, only a bit of physical chemistry... Let us suppose we are calculating The formation heat (aka formation enthalpy, DeltaH_f) of wurtzite ZnO. First of all, what is it the formation enthalpy? Suppose that we are not very rigorous, we may say "the energy gained to form ZnO from Zn and O in their standard state". We may consider therefore this chemical process: Zn(metal)+O2(gas)-->ZnO(wurtzite) How can we calculate such an energy? Well, all chemical "Delta" quantities are defined as a difference between some final state quantity (free energy, enthalpy, ...) and the related initial state quantity. If we consider negligible the PV contribution to the above chemical process (H = U+PV), we can estimate formation heats as differences of total energies calculated in supercells: DeltaH_f (ZnO) = E(ZnO) - E(Zn) - E(O2) You must only be sure that the number of atoms in all the supercells is fully consistent with your calculation: ZnO(wurtzite): 4 atoms (2 ZnO units) Zn(metal, hcp): 1 atom O2 molecule: 2 atoms Your final equation is therefore DeltaH_f (ZnO) = E(ZnO) - 2*E(Zn) - E(O2) Modify it according to your purpose... HTH Giuseppe On Tuesday 19 June 2012 11:21:54 debbichi mourad wrote: > Dear pwscf users. > How to calculate the formation enthalpy, which command? I can added to the > input? best regards >? > DEBBICHI Mourad > Unit? de Recherche Physique des Solides,99/UR/13-19, > D?partement de Physique, Facult? des Science de Monastir, > Avenue de l'Environnement 5019, Monastir Tunisie. > t?l:+21697487042 > mourad_fsm at yahoo.fr -- ******************************************************** - Article premier - Les hommes naissent et demeurent libres et ?gaux en droits. Les distinctions sociales ne peuvent ?tre fond?es que sur l'utilit? commune - Article 2 - Le but de toute association politique est la conservation des droits naturels et imprescriptibles de l'homme. Ces droits sont la libert?, la propri?t?, la s?ret? et la r?sistance ? l'oppression. ******************************************************** ? Giuseppe Mattioli? ? ? ? ? ? ? ? ? ? ? ? ? ? ? CNR - ISTITUTO DI STRUTTURA DELLA MATERIA? ? v. Salaria Km 29,300 - C.P. 10? ? ? ? ? ? ? ? ? I 00015 - Monterotondo Stazione (RM)? ? ? ? ? ? Tel + 39 06 90672836 - Fax +39 06 90672316? ? ? E-mail: <giuseppe.mattioli at ism.cnr.it> -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20120619/6001a050/attachment-0001.htm
