Just to explain the mechanism how a U for "semicore" 3d states (Sn, but
also Zn in ZnO or Ge, ...):
Usually, U shifts occupied d-states down by U/2 and unoccupied d-states
up by U/2. This is the mechanism eg. in NiO.
However, for these fully occupied states, the effect of U is much
smaller, since ther is no "reoccupation" possible.
Now: how can the gap, which is formed between O-2p states at the VBM and
Sn-s states at the CBM be affected by a U for d states ??
The effect is very "indirect": The U localizes the d-semicore states
even more, this leads to a better shielding of the nucleus as seen by
the very diffuse 4s (for Zn) states, i.e. this means that these s states
are less attracted by the nucleus and increase their energy. Thus the
larger gap.
It is clearly not the correct physics, as even an exact DFT functional
should not give you the proper gap as difference of VBM and CBM (without
the xc-discontinuity), but might mimic it well if the U is chosen
properly (and very large).
Am 28.01.2020 um 17:11 schrieb Laurence Marks:
An important point Peter pointed out to me some years ago.
Remember that electrons are dumb. They go where they want; we think
about them as s,p,d etc. I suspect that your Sn d-states should be
semi-core (-1.5Ryd) and largely uneffected by +U
What you (and perhaps your cited paper) are probably really doing is
changing the tails of the S states that reach into the Sn RMT. These
have the symmetry of d-states, so are counted as such and "see" the
Hubbard term. This is not really correct physics, more a fudge to avoid
have too much covalency.
On Tue, Jan 28, 2020 at 8:36 AM shamik chakrabarti
<shamik15041...@gmail.com <mailto:shamik15041...@gmail.com>> wrote:
I want to simulate Li intercalation voltage in SnS2. But for that I
need to simulate pristine SnS2 properly....
On Tue, Jan 28, 2020, 19:46 Laurence Marks <laurence.ma...@gmail.com
<mailto:laurence.ma...@gmail.com>> wrote:
Reducing the RMT by 30% is somewhat large.
The key question is what are you trying to do? Reproducing a
result with Vasp is not good science if that is your purpose.
Without that information I doubt that anyone can provide useful
advice
_____
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>
On Tue, Jan 28, 2020, 08:11 shamik chakrabarti
<shamik15041...@gmail.com <mailto:shamik15041...@gmail.com>> wrote:
Dear Professor Laurence and wien2k users,
with reference to my
earlier mail on SnS2, I have checked the change in RMT (for
avoiding Ghostband) with U and corresponding band gap. The
details are as follows;
U = 7 eV RMT reduction 6% Band gap = 1.460 eV
U = 8 eV RMT reduction 15% Band gap= 1.475 eV
U= 9 eV RMT reduction 30% Band gap = 1.512 eV
I have not able to reproduce the band gap ~ 2.1 eV as
computed earlier using Vasp (Phys. Chem. Chem. Phys., 2016,
18, 318). Also, whether 30% reduction of RMT is acceptable???
Looking forward to further guidance from you.
with regards,
--
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India
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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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