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

[Nam Tran]

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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