[Pw_forum] relaxation and TS

[vega lew]

  Through the relaxation of a oxygen molecule on a surface by QE4.2, it 
dissociated and adsorbed on the surface. The scf energy of each step has 
decreased in compared with the previous step until the relaxation 
completed. Now, can one say that there is not any TS for O2 dissociation 
here ?

Probably not. The potential energy surface might be not very corrugated 
and the energy barrier for the dissociation might be not very large, so 
that the dissociation of O2 could happen in a relax calculation. I think 
there might be a very minute TS in the dissociation process.

Or is the reaction spontaneous ?

If the total energy of system goes down continuously and the adsorption 
energy of dissociated state is lower than the one of molecular state, 
you could say the reaction is favorable. Whether it is spontaneous, it 
is depend on how large of the energy barrier.


If there was a TS in this procedure (dissociation and adsorption of O2) 
would the optimization algorithm of QE4.2 stop the work or continue ?

If there is only one bond broken in the process you considered, you 
could try constrained optimization technique. For you information, 
please refer to B.Hammer (Hammer, B.; Jacobsen, K. W.; Norskov, J. K. 
Phys. Rev. Lett. 1992, 69, 1971) or PJ Hu's work. (Alavi, A.; Hu, P.; 
Deutsch, T.; Silvestrelli, P. L.; Hutter, J. Phys. Rev. Lett. 1998, 80, 
3650). Or recent developed method by ZP Liu (J. Chem. Theory Comput. 
2010, 6, 1136--1144 )

hope helps,

best

vega
On 09/29/10 22:59, Masoud Nahali wrote:
>
> Dear PWscf Users
>
> Through the relaxation of a oxygen molecule on a surface by QE4.2, it 
> dissociated and adsorbed on the surface. The scf energy of each step 
> has decreased in compared with the previous step until the relaxation 
> completed. Now, can one say that there is not any TS for O2 
> dissociation here ? Or is the reaction spontaneous ? If there was a TS 
> in this procedure (dissociation and adsorption of O2) would the 
> optimization algorithm of QE4.2 stop the work or continue ? Any help 
> would be *appreciate*. Many Thanks
> /-----------------/
> /Masoud Nahali/
> //PhD Student of Physical Chemistry
> Sharif University of Technology/
>
> /
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum

-- 

================================================
Vega Lew ( weijia liu)
Graduate student
State Key Laboratory of Materials-oriented Chemical Engineering
Nanjing University of Technology, 210009, Nanjing, China
***************************************************************
Email: vegalew at gmail.com
Office: Room A705, Technical Innovation Building,
Xinmofan Road 5#, Nanjing, China
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