[Wien] structure of oxygen molecule

[Peter Blaha]

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
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