[QE-users] Adsorption studies

[Hande Toffoli]

Dear Paolo,

Assuming everything was set up correctly (for which I would have to see
your input files), the magnitude of the adsorption energy is way too large
to be accounted for by dipole corrections. What I would suggest is for you
to isolate the TiO2 slab from Anastase_Surface_without_H_anisole_1.out and
run an scf calculation on it. I would then see what the difference is with
the final energy you obtain from Anastase_Surface_without_H.out. If the
difference is very large, there's your answer. This suggestion is triggered
by the observation that the reconstruction on the "bottom" surface of the
slabs in the two output files appears different. This may not be the answer
but worth a shot.

Beyond this, there are a couple things to note about your calculations. The
first one is that it appears that you are not using van der Waals
corrections. Since your molecules are perpendicular, it shouldn't matter
that much but most commonly, such a molecule would adsorb in the parallel
configuration, so presumably you will investigate that configuration as
well. So it may be worthwhile investigating the effect of some vdW schemes.
Secondly, your molecule appears to travel a lot on the slab during the
geometry optimization. This is a little unusual, I would investigate this.

Hope this helps.
Hande

On Wed, Jul 25, 2018 at 7:01 PM, Paolo Costa <paolo.costa85 at gmail.com>
wrote:

>
> Dear experts,
>
> I got nonsense value of adsorption energy by computing 4-iodoanisole on
> top of TiO2 anastase surface (101).
> By calculating : (Esurface+anisole)-Eanisole-Esurface, I got an
> adsoprtion energy of 0.66 ry (8.98 eV), which is too high.
> Now I am trying to apply the dipole correction to see if this is the
> problem causing an unusual adsorption energy.
> In attachment I put the output files.
> I would be glad to receive any suggestions to understand the problem.
>
> Thanks.
>
> Paolo
> --
> Paolo Costa, Ph.D.
> Postdoctoral Researcher
> Department of Chemistry and Biomolecular Sciences
> University of Ottawa
> 10 Marie Curie, Ottawa, ON K1N 6N5, Canada
> Room number: DRO 326 (D'Iorio Hall)
>
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-- 
Hande Toffoli
Department of Physics
Office 439
Middle East Technical University
Ankara 06800, Turkey
Tel : +90 312 210 3264
https://www.compmatsci.com/
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