[QE-users] Wrong adsorption energy

[Stefano de Gironcoli]

two things I think might be the origin of strange results.

your ethyl-anion is charged. the code introduce a compensating 
background that should cancel out when you calculate the adsortion 
energy but you are using different cells in the two charged 
configurations. so something does not cancel out as it should.

there might be some vdW interaction contributing to the physisorption. I 
see no inclusion of vdW corrections or use of vdW-aware functionals in 
your calculations.


best


stefano


On 08/03/2018 15:50, Laurens Siemons wrote:
>
> Dear all,
>
>
> I'm calculating parameters like adsorption energy, geometric 
> parameters, NMR chemical shifts of adsorbates on a surface. In this 
> specific case I calculated the adsorption energy of an ethyl anion on 
> an anatase 001 surface of titania. I got the following energies:
>
>
> E_surface + adsorbate = -4301.05337244
>
> E_surface = -4258.9387474
>
> E_adsorbate = -42.37757742
>
>
> So E_ads = E_surface + adsorbate - (E_surface + E_adsorbate ) = 0.26
>
>
> Now this seems wrong. If E_ads is positive, so adsorption is not 
> favourable, then the ethyl-anion should migrate away from the surface 
> in the relax calculation of a001cti. correct? I executed the three 
> calculations with the exact same parameters as the other ones so I 
> don't see how this is possible. I attached my input files of the 
> calculations. I hope someone can guide me through this.
>
>
> Thanks in advance,
>
> Laurens Siemons
>
> Master student chemistry
>
> University of Antwerp
>
>
>
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