[QE-users] Adsorption energy between charged slab + anion

[Marcelo Albuquerque]

Dears Giuseppe, Stefano, and Nam Tram

Sorry, but I'm just thinking about how to sort this issue out.

Would that kind of problem be circumvented by using the QE's ENVIRON puglin?
Or to avoid the generated macroscopic electric field, would be a good idea
to use a charged plate (variable gate in pw.x input) placed close to the
molecule?


Thank you all in advance.


Best regards,

*       Marcelo Albuquerque*

*        Ph.D. Candidate*

*      Physics Institute*

*Fluminense Federal University (UFF)*
*       Niterói/RJ - Brazil*



On Tue, Feb 23, 2021 at 8:01 AM Nam Tran wrote:

> Dear Giuseppe and Stefano,
>
> Thank you so much for your reply.
> I guess I have to rephrase my problem and think about it in a different
> way.
>
> Best regards
> Nam
>
>
> > On Feb 23, 2021, at 8:22 PM, Giuseppe Mattioli <
> giuseppe.mattioli at ism.cnr.it> wrote:
> >
> > ?
> > Dear Nam
> > If you forget the DFT problem of unbound electrons in anions (which is
> not a chemical or physical problem) and think about the chemistry, there is
> no real process that ends with a nitrate anion in gas phase, AFAIK.
> Desorption may rather involve a neutral NO2 molecule, depending on the
> surface redox chemistry. Of course release of anions in solution is
> possible, but you should simulate a (proper or implicit) solvation
> environment.
> > HTH
> > Giuseppe
> >
> > Quoting Stefano Baroni <baroni at sissa.it>:
> >
> >> If the anion stays charged, which is an issue by itself in DFT, the
> distance will never be large enough, because the slab will generate a
> macroscopic electric field. sb
> >>
> >> ___
> >> Stefano Baroni, Trieste -- http://stefano.baroni.me
> >>
> >>>> On 23 Feb 2021, at 07:05, Nam Tran <vnt981 at uowmail.edu.au> wrote:
> >>>
> >>> ?
> >>> Dear QE users,
> >>>
> >>> I would like to calculate the adsorption energy of a negative anion
> NO3- with a positive slab (The total system is neutral). I cannot use the
> convention formula Eds = E(slab+anion) - E(slab) - E(anion) because of the
> charge compensation when calculating the energy of charged slab and charge
> adsorbate.
> >>>
> >>> As the total system (slab+anion) is neutral, I wonder if it is
> possible to just move the molecule far away from the slab (make sure that
> vacuum in z-direction is large enough), and calculate the energy difference
> i.e., one of them the molecule is far away from the surface and in the
> other one the molecule adsorbed on the surface.
> >>>
> >>>
> >>> Best regards
> >>> Nam
> >>>
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> >
> > GIUSEPPE MATTIOLI
> > CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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