[QE-users] Adsorption energy studies

[Paolo Costa]

Thank you Giovanni for your quick reply.
I will apply the dipole correction as you suggested.

Paolo

2018-07-25 14:14 GMT-04:00 Giovanni Cantele <giovanni.cantele at spin.cnr.it>:

> In you are dealing with asymmetric slabs, dipole correction might be
> important. Some adsorbates are just conceived to change the work function
> of a material, thus representing dipole layers added on the top of a
> surface. The induced dipole can make the vacuum levels in the two sides of
> the slab rather different
> Giovanni
>
> Inviato da iPhone
>
> Il giorno 25 lug 2018, alle ore 20:05, Paolo Costa <
> paolo.costa85 at gmail.com> ha scritto:
>
> 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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-- 
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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