[QE-users] Adsorption energy studies

[Giovanni Cantele]

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
>>             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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>> 
>> 
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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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