I would answer it differently:
No, it does not really make sense to use LDA+U for an atom; but there
are not many other chances to calculate formation or cohesive energies.
For such quantities one MUST do all calculations with exactly the same
calculational parameters and of course also with identical
DFT-approximations.
In all cases, where for one or the other system a certain approximation
is not very good, the corresponding E-differences are of course very
problematic.
So if you compare a TM oxide with free TM and O atoms, all
approximations must be the same.
Of course for a TMO GGA+U is probably much better, but I would NOT say
this for a free atom.
You can test the sensitivity of your results be repeating the same
E-difference using GGA (or even better a meta-GGA), i.e. you treat the
atom more meaningful, but may even have a "metallic" TMO.
The situation is similar for a formation energy of a TMO with respect to
the metallic element and O2. GGA+U for bcc Fe with a sizable U gives
magnetic moments up to 3 mB !
Am 13.05.2016 um 19:42 schrieb Zsolt Rak:
Does it make sense to perform LDA+U/GGA+U calculation on free, isolated
atom?
On Thu, May 12, 2016 at 11:47 AM, Laurence Marks
<l-ma...@northwestern.edu <mailto:l-ma...@northwestern.edu>> wrote:
To obtain reasonable results you have to be fully consistent with
everything, e.g. RMT, RKMAX, U's etc.
On Thu, May 12, 2016 at 10:37 AM, Zsolt Rak <zsolt....@gmail.com
<mailto:zsolt....@gmail.com>> wrote:
Dear users,
I am calculating the cohesive energy of a series of transition
metal (TM) oxides and I have the following questions: because
the energy of the TMO is calculated within the LDA+U framework
should I use the same LDA+U for the free atoms? Does it make
sense to subtract LDA+U/GGA+U energies of oxides from LDA/GGA
energies of free atoms? Does it make sense to use LDA+U/GGA+U
for free atom calculations?
Thanks,
Zsolt
--
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what
nobody else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu
<http://www.numis.northwestern.edu> ; Corrosion in 4D:
MURI4D.numis.northwestern.edu <http://MURI4D.numis.northwestern.edu>
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equity, www.cfw.org/100-percent <http://www.cfw.org/100-percent>
Co-Editor, Acta Cryst A
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