[Pw_forum] (no subject)

[Giuseppe Mattioli]

Dear Mourad

> How to obtain the total energy E(Zn) and E(O2) ?

E(Zn) = total energy of a Zn(hcp) unit cell. You have to perform this calculation. 

E(O2) = an O2 molecule in an adequately large cubic supercell. You have to perform this calculation.

Giuseppe

On Tuesday 19 June 2012 14:10:42 debbichi mourad wrote:
> Thank you Giuseppe.
> How to obtain the total energy E(Zn) and E(O2) ?
> 
> 
>  
> DEBBICHI Mourad
> Unité de Recherche Physique des Solides,99/UR/13-19,
> Département de Physique, Faculté des Science de Monastir,
> Avenue de l'Environnement 5019, Monastir Tunisie.
> tél:+21697487042
> mourad_fsm at yahoo.fr
> 
> 
> ________________________________
>  De : Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it>
> À : debbichi mourad <mourad_fsm at yahoo.fr>; PWSCF Forum <pw_forum at pwscf.org>
> Envoyé 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
> > Unité de Recherche Physique des Solides,99/UR/13-19,
> > Département de Physique, Faculté des Science de Monastir,
> > Avenue de l'Environnement 5019, Monastir Tunisie.
> > tél:+21697487042
> > mourad_fsm at yahoo.fr

-- 
********************************************************
- Article premier - Les hommes naissent et demeurent
libres et ègaux en droits. Les distinctions sociales
ne peuvent être fondèes que sur l'utilitè commune
- Article 2 - Le but de toute association politique
est la conservation des droits naturels et 
imprescriptibles de l'homme. Ces droits sont la libertè,
la propriètè, la sùretè et la rèsistance à 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>