[Wien] Extract energy contribution of a single atom

[Peter Blaha]

It is (to some extend) justified to take this energy difference (1 Ry/3) 
by assuming that the energy conributions of all other atoms do not 
change between configuration 1 and 2, because only the different 
magnetic arrangemnt of the Ni atoms cause this difference. This is of 
course not "exact", but a plausible assumption. Thus this "sloppy" notation.

Personally, I would give energy differences per formula unit, except 
when you compare formation energies of compounds with different 
stoichiometry (eg. one with 3 Ni the other one with 4 Ni).



Am 15.05.2020 um 04:23 schrieb Fan:
> Thank you for your reply, Prof.  Marks. I am afraid I didn't express 
> myself clearly. My question is how they get such a quantity like 
> "meV/Ni". For instance, in my experience, the energy of the system 
> La4Ni3O8 in that paper should be about -170000 Ry. Of course, this value 
> is meaningful only when you compare it with another energy, which means 
> what makes sense is the energy difference. Say we have another 
> configuration with an energy -169999 Ry (under the same parameters). The 
> energy difference is 1 Ry. This is already clear to me, so why and more 
> importantly, how they get energy difference per Ni. Did they know the 
> energy contribution of Ni to the total energy? like -5000 Ry? This 
> doesn't make sense to me. Or they just gave 1 Ry/3 (number of Ni), if so 
> how to justify this action, after all, La and O could also have 
> contributions to the 1 Ry.
> 
> with regards,
> 
> Fan
> 
> On Thu, May 14, 2020 at 11:55 PM Laurence Marks 
> <laurence.marks at gmail.com <mailto:laurence.marks at gmail.com>> wrote:
> 
>     Energy is always a relative term, so you have to reference it. In
>     thermodynamics the standard reference is STP; in DFT you can chose
>     anything relevant so long as you clearly state what you are doing. 
>     Since they want to compare the energies for different spin states,
>     they chose the lowest (which is reasonable).
> 
>     N.B., of course comparisons have to be with identical technical
>     parameters, e.g. RKMAX, RMT, GMAX, U ...
> 
>     On Thu, May 14, 2020 at 10:41 AM Fan <fxinwei123 at gmail.com
>     <mailto:fxinwei123 at gmail.com>> wrote:
> 
>         Dear WIEN2k users,
> 
>         Recently I read several papers, which explore the ground state
>         with wien2k by comparing the energy contribution of a single
>         atom. For example, in table1 of reference
> 
>         https://iopscience.iop.org/article/10.1088/0953-8984/24/40/405502 <https://urldefense.com/v3/__https://iopscience.iop.org/article/10.1088/0953-8984/24/40/405502__;!!Dq0X2DkFhyF93HkjWTBQKhk!FpC4rbUdTRuV5JHsAv-Y9PMuqlVfRKBfHcy-qYNThCYdEbj0EcewcYZ6FSepiI4OZn_sGg$>
> 
>         they were looking for energy advantageous magnetic configuration
>         by the energy difference per Ni.
>         I was wondering how they did that, is this achievable in wien2k?
>         or they just calculated the total energy difference and then
>         divided by the number of a specific atom?  And why they did this
>         instead of comparing the total energy or energy difference per
>         formula, which are more straightforward and sensible to me.
> 
>         Hope someone can enlighten me.
> 
>         Fan
>         _______________________________________________
>         Wien mailing list
>         Wien at zeus.theochem.tuwien.ac.at
>         <mailto:Wien at zeus.theochem.tuwien.ac.at>
>         https://urldefense.com/v3/__http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien__;!!Dq0X2DkFhyF93HkjWTBQKhk!FpC4rbUdTRuV5JHsAv-Y9PMuqlVfRKBfHcy-qYNThCYdEbj0EcewcYZ6FSepiI5sMHANgA$
> 
>         SEARCH the MAILING-LIST at:
>         https://urldefense.com/v3/__http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html__;!!Dq0X2DkFhyF93HkjWTBQKhk!FpC4rbUdTRuV5JHsAv-Y9PMuqlVfRKBfHcy-qYNThCYdEbj0EcewcYZ6FSepiI5rWLPwMw$
> 
> 
> 
> 
>     -- 
>     Professor Laurence Marks
>     Department of Materials Science and Engineering
>     Northwestern University
>     www.numis.northwestern.edu <http://www.numis.northwestern.edu/>
>     Corrosion in 4D: www.numis.northwestern.edu/MURI
>     <http://www.numis.northwestern.edu/MURI>
>     Co-Editor, Acta Cryst A
>     "Research is to see what everybody else has seen, and to think what
>     nobody else has thought"
>     Albert Szent-Gyorgi
>     _______________________________________________
>     Wien mailing list
>     Wien at zeus.theochem.tuwien.ac.at <mailto:Wien at zeus.theochem.tuwien.ac.at>
>     http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>     SEARCH the MAILING-LIST at:
>     http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
> 
> 
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> SEARCH the MAILING-LIST at:  http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
> 

-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671