[QE-users] Wrong adsorption energy

[Laurens Siemons]

Thank you all for your quick response.


I'm running a calculation now like Evren Ataman suggested. By doing this the problem of the compensating background should be resolved as well.

The reason I'm not using vdw corrections is based on an article (doi: 10.1021/jz501050f) where they did calculations with and without these corrections. There conclusion is that the corrections are negligible.


Kind regards,

Laurens Siemons

________________________________
Van: users <users-bounces at lists.quantum-espresso.org> namens Stefano de Gironcoli <degironc at sissa.it>
Verzonden: donderdag 8 maart 2018 16:19
Aan: users at lists.quantum-espresso.org
Onderwerp: Re: [QE-users] Wrong adsorption energy


two things I think might be the origin of strange results.



your ethyl-anion is charged. the code introduce a compensating background that should cancel out when you calculate the adsortion energy but you are using different cells in the two charged configurations. so something does not cancel out as it should.



there might be some vdW interaction contributing to the physisorption. I see no inclusion of vdW corrections or use of vdW-aware functionals in your calculations.


best


stefano

On 08/03/2018 15:50, Laurens Siemons wrote:

Dear all,


I'm calculating parameters like adsorption energy, geometric parameters, NMR chemical shifts of adsorbates on a surface. In this specific case I calculated the adsorption energy of an ethyl anion on an anatase 001 surface of titania. I got the following energies:


Esurface + adsorbate = -4301.05337244

Esurface = -4258.9387474

Eadsorbate = -42.37757742


So Eads = Esurface + adsorbate - (Esurface + Eadsorbate) = 0.26


Now this seems wrong. If Eads is positive, so adsorption is not favourable, then the ethyl-anion should migrate away from the surface in the relax calculation of a001cti. correct? I executed the three calculations with the exact same parameters as the other ones so I don't see how this is possible. I attached my input files of the calculations. I hope someone can guide me through this.


Thanks in advance,

Laurens Siemons

Master student chemistry

University of Antwerp




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