Dear WIEN2K users, I am doing some electronic structure calculations on graphene sheet using WIEN2K. I am wondering if anybody can help me about my problem. The problem is as follow:
My calculation shows that the total charge of carbon atom in muffin-tin sphere is about 4 electrons. It means that about 2 electron of Carbon atom is distributed in interstitial region. Is it correct for graphene? I checked it for Diamond. The result was same!!! If it is not correct How can i decrease the interstitial charges in my system. Is it possible? I should mention that, for test calculation, i did SCF run for Iron Fe. CTO : TOTAL INTERSTITIAL CHARGE= 1.0301020 TOTAL CHARGE IN SPHERE 1 = 24.9698980 As you see the total charge in muffin-tin sphere is about 25 electrons. Thank you very much for your help. Best regards,
This is determined by the electron density and the RMT. If you increase the RMT, you will have more inside the muffin-tin, but of course you cannot do too much of this!
There is no real physics in how much density there is in the muffin tin, this has little meaning. Hence in reality you have no problem -- what matters is where in 3D the electrons are, i.e. sp2 versus sp3.
In fact, what you obtain is certainly values like (consider atom 1 as
carbon):
CHA001 = 1.7 (which gives you the number of valence electron inside the
MT sphere)
and
CTO001 = 3.7 (which gives you the number of total electron inside de MT
sphere)
So as you mention 2 electrons are missing (in comparison to the atomic
electronic structure 1s2 2s2 2p2), but the interaction is strong between
carbon atoms (same electronegativity) and then an important part of the
electronic density is in between the atoms (i.e. in the interstitial
region). So a significant part of the charge should be in the
interstitial region.
Lets take one of my examples to illustrate this feature. Sometimes ago I
did calculation on vanadate compounds and the charge in the MT sphere of
vanadium was as follow:
CHA = 1.818 for a vanadium 5+
CHA = 1.874 for a vanadium 4.5+
CHA = 1.899 for a vanadium 4+
As you see an increase of 1 electron in terms of formal charge lead to
an increase of 0.081 electrons in the MT sphere !!!
So the variation is very small although in such a strong change from V5+
(with 3d0 electronic configuration) and V4+ (3d1).
So you can imagine that between graphene and diamond the change is
smaller (same oxidation degree but different hybridation).
To conclude, when you are interested in the "real" charge of an atom you
have to consider Bader charges or related tools (look at AIM program in
WIEN2k).
Best regards
Xavier
My name is Dr Abderrahmane Reggad. I'm a 54 year old and I am a researcher in materials' sciences. 
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