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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