1) Should I always run -sp calculation for atomization energy? I read
for O2, N2 etc it is necessary but for other elements like Mg, Ba, Ge or
Si) I am not sure.
You should run spin-polarized, if it is necessary. This is for
free atoms: open shell atoms (Li-yes, Be-no;B-yes,.....)
molecules: only for molecules with unpaired electrons: O2 (2 unpaired
electrons), NO-yes, but not for N2
for formation energy (solids): only for magnetic solids (Fe,Co,Ni)
2) As we know Mg is stable in hcp while O2 is in cubic.
For formation energy (for example MgO) I would need to run Mg and O2 in
their stable structures,hcp <https://en.wikipedia.org/wiki/Magnesium>
and cubic <https://en.wikipedia.org/wiki/Oxygen>, respectively.
You need to simulate bulk hcp Mg (including volume optimization !!!),
but O2 we simulate as molecule (big box, 1-k, but with force optimization
to calculate the theoretical bond length).
In experiment during preparation of MgO; MgO is in equillibrium with
bulk Mg and O2 molecules (not the O2-solid).
For cohesive energies: I would need to run Mg and O2 for a large cubical
box ~15Angs with one k-point. Am I going to the right direction?
Yes.
I want to reproduce thermodynamical stability of BaZrO3:
http://pubs.rsc.org/-/content/articlehtml/2016/cp/c6cp04065a
I ran Ba in its stable from (BCC <https://en.wikipedia.org/wiki/Barium>)
and O2 (bond length 1.21Ang) in Cubic for formation energy.
And Ba and O2 in a cubic box of 15 Ang for atomization energy (Ba
without -sp while O2 with -sp).
Hope I explained my query more clearly now.
Barium
The most common naturally occurring minerals of barium are barite
(barium sulfate, BaSO4) and witherite (barium ...
<https://en.wikipedia.org/wiki/Barium>
Regards
Chin
You have to distinguish between an
atomization energy and a formation energy (from stable elementary
forms).
For example for MgO you need to calculate the free atoms Mg and O
(spinpolarized) for the atomization energy, as described by you.
For the formation energy, you would calculate hcp Mg (vol+c/a
optimization) and the O2 molecule.
And if you are interested in phase stability, you would need to
calculate in addition MgO not only in NaCl structure, but in as many as
possible other structures (CsCl, ZnO, GaAs, ....).
PS: The PBE functional does not always give the correct ground state
structure !!!
Am 02.11.2017 um 00:11 schrieb chin Sabsu:
>
>
> Dear Sir
>
>
> I want to run scf for oxygen molecule.
>
> I found a contradiction in the literature about the structure of Oxygen
> so I am asking here for any comment.
>
>
> In many of the paper published using Wien2k, authors used O2 in 15Ang
> cubic box (results are matching with the experimental values in the
> published papers) while in one of the thread Prof. Peter suggested to
> create it in F cell with (a=b)<C.
>
[1]https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg16458.html
>
>
> [2]
> http://zeus.theochem.tuwien.ac.at/pipermail/wien/2003-October/000880.html
>
>
>
> Could you please tell me which one is better. It is to compute formation
> energy of a system and cohesive energy of Oxygen.
>
> Another question is: for one k-point calculation, should I use 1 in the
> "x kgen" or (0 0 0 >>>> it may be at Gamma).
>
> Kind regards
> Chin
>
>
>
>
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--
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300 FAX: +43-1-58801-165982
Email: bl...@theochem.tuwien.ac.at WIEN2k: http://www.wien2k.at
WWW:
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