[Wien] structure of oxygen molecule

[Peter Blaha]

> 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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> 
> -- 
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300            FAX: +43-1-58801-165982
> Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
> WWW:
> http://www.imc.tuwien.ac.at/tc_blaha------------------------------------------------------------------------- 
> 
> 
> 
> 
> 

-- 
--------------------------------------------------------------------------
Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW: 
http://www.imc.tuwien.ac.at/tc_blaha-------------------------------------------------------------------------