[Wien] Extract energy contribution of a single atom

[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>
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> 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
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>
>
> --
> Professor Laurence Marks
> Department of Materials Science and Engineering
> Northwestern University
> www.numis.northwestern.edu
> Corrosion in 4D: 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
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