[Wien] Extract energy contribution of a single atom

Fri May 15 11:11:47 CEST 2020

Thank you for confirming it, Prof. Blaha. I agree with you, energy
difference per formula unit indeed seems a better choice.

With regards

Fan

On Fri, May 15, 2020 at 2:21 PM Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:

> 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
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> >
> >
> >
> >
> >     --
> >     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
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>
> --
> Peter Blaha
> Inst.Materials Chemistry
> TU Vienna
> Getreidemarkt 9
> A-1060 Vienna
> Austria
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