[QE-users] Wrong adsorption energy

[Stefano Baroni]

not necessarily, if there is a barrier (after all, there are plenty of exothermic chemical reactions, without which no fire would exist!) — Stefano B

> On 8 Mar 2018, at 15:50, Laurens Siemons <laurenssiemons at hotmail.be> 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:
> 
> Esurface + adsorbate = -4301.05337244
> Esurface = -4258.9387474
> Eadsorbate = -42.37757742
> 
> So Eads = Esurface + adsorbate - (Esurface + Eadsorbate) = 0.26
> 
> Now this seems wrong. If Eads 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
> 
> <a001cti.rx.in><anatase001-2x2-4.rx.in><ethyl-anion.rx.in>_______________________________________________
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—
Stefano Baroni -  SISSA, Trieste - http://stefano.baroni.me, stefanobaroni (skype)

There are two ways of doing a theoretical calculation: you should have either a clear physical model in mind, or a rigorous mathematical basis. You have neither. [E. Fermi to F.J. Dyson, as humbly reported by the latter]

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