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.ma...@gmail.com <mailto:laurence.ma...@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 <fxinwei...@gmail.com
<mailto:fxinwei...@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>
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"Research is to see what everybody else has seen, and to think what
nobody else has thought"
Albert Szent-Gyorgi
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