[QE-users] Adsorption energy studies

[Paolo Costa]

Hi Giovanni,

thanks a lot for your quick reply.
I guess you are definetely right, I did not recognize such error. I will
put right way the calculation of the surface allowing the relax of all the
atoms. I will let you know the results.

By the way, do you think that the dipole correction is always necessary for
adsorption studies?

Thanks again.

Paolo

2018-07-25 13:21 GMT-04:00 Giovanni Cantele <giovanni.cantele at spin.cnr.it>:

> I cannot visualise your structures at the moment, however one first issue,
> concerning the adsorption energy calculation is that it seems that in the
> system WITOUTH
> the molecule you fixed some Ti/O layers, that are instead free to relax in
> the adsorbed system. As such, the run with the molecule is able to lower
> the total energy
> also by allowing those atoms (a lot!), that were fixed in the other run,
> to change their positions. The result is that the -0.66 Ry contain also the
> energy gain of
> the “free” surface when you let those atoms to relax towards a lower
> energy configuration. So, one first check would bee to see whether the
> atomic positions
> of those atoms changed a lot (for example I see the z of one Ti atom equal
> to 15.819807000 when it is fixed, and 16.095206282 when it is allowed to
> relax, this is a change
> of ~0.3 A -> 2% of the initial coordinate, that summed over all those
> atoms might make a difference!).
> In any case I would try to make a surface (with no molecule) run where all
> atoms are allowed to relax and see how much energy is gained with respect
> to your run.
>
> I could give you more hints tomorrow, if I’m able to visualise the
> structures
>
> Giovanni
>
> --
>
> Giovanni Cantele, PhD
>
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
>
> e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
>             gcantele at gmail.com
> Phone: +39 081 676910
> Skype contact: giocan74
> Web page: https://sites.google.com/view/giovanni-cantele
>
> On 25 Jul 2018, at 19:07, 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 the following link you can find the output files:
> https://www.dropbox.com/sh/edijwg1kyp7gx31/AACD7Up1XIIULbJFToLNqsUra?dl=0
>
> I would be glad to receive any suggestions to understand the problem.
>
> Thanks.
>
> Paolo
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-- 
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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