[QE-users] Adsorption energy studies

[Giovanni Cantele]

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 <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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