[Pw_forum] enthalpy of adsorbtion of o2 molecule on a ZnO supercell

[Prasenjit Ghosh]

Dear Meysam,

When you do a supercell calculation you do not need to relax the
lattice parameters because the cell vectors perpendicular to the
surface is ficticious in the sense that you simply use a value large
enough so that the periodic images perpendicular to the surface do not
interact with each other.
The inplane lattice vectors are determined by your theoretically
obtained bulk lattice parameter for ZnO.

So you should follow the procedure suggested by Mohnish.

Just another addition, all the calculations, the ZnO surface, O2+ZnO
surface and the O2 molecule in vacuum (the gas phase) should be done
using the same supercell. Also be careful when you do calculations for
O2 molecule in gas phase, you should do a spin polarized calculation
becase the ground state of O2 is spin triplet.

Hope this helps.

Prasenjit.

On 14 October 2010 23:00, mohnish pandey <mohnish.iitk at gmail.com> wrote:
> Dear Meysam,
>                         First you relax the supecell using "relax"
> calculation, it will make all the atoms to attain an equilibrium position.
> Then  adsorb the atom (make it close enough so that your surface is
> interacting with the adorbate) and make the "relaax" calculation again. The
> energy that you get from latter step subtract the "former energy of the
> supercell+energy of the isolated adsorbate"..This difference should give the
> adsorption energy. In fact I have not done any adsorption calculations but
> intuitively what I have said seems correct to me.
>
> On Thu, Oct 14, 2010 at 5:08 PM, meysam pazoki <m_pazoki at physics.sharif.edu>
> wrote:
>>
>> Dear PWSCF users
>>
>> I want to calculte the enthalpy of adsorbtion of o2 molecule on the
>> surface of a ZnO.Can i use variable cell relaxation for the supercell and
>> use the enthalpy that printed in output file?
>> I can also run a series of scf jobs with different cell volumes,and then
>> calculate the pressure of system from E-V diagram and then calculate
>> enthalpy by H=E+PV from my data.Is it also true?
>>
>> Thanks
>> Best Regards
>> Meysam Pazoki
>> SUT
>>
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>
>
>
> --
> Regards,
> MOHNISH,
> -----------------------------------------------------------------
> Mohnish Pandey
> Y6927262,5th Year dual degree student,
> Department of Chemical Engineering,
> IIT KANPUR, UP, INDIA
> -----------------------------------------------------------------
>
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PRASENJIT GHOSH,
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