[Wien] Bader analysis

[Laurence Marks]

It is important to recognize that "2+" and "2-" are the valences, NOT
the charges. The term "formal charges" is in my opinion dangerously
misleading. Valences go back to Pauling, and are an insight into the
bonding. You might find
Surface Science 606 (2012) 344 and the references therein useful, or
do a google search on "Bond Valence" which is the appropriate modern
term.

The Bader charges are different, not really connected. They are a
measure of how the charges (as against valences) are distributed. If
you found Bader charges of (for instance) +1.5/-1.5 that would
correspond to a very ionic compound, whereas with +0.12/-0.12 you have
a covalent compound. (Please note that I have put the sign in front
when I mean real electrostatic charges, as against after when it is a
valence -- this is deliberate.)

The fact that some of the charge is in the interstitial, i.e. outside
the muffin-tins is not relevant to much.

N.B., if you do "x nn ; grep -e Bond *tnn " you get the Bond Valences
for oxides and a few other combinations, not sure about FeTe.

On Mon, Feb 11, 2013 at 11:13 AM, Hefei Hu <huhefei at gmail.com> wrote:
> Dear Wien2k users,
>
> I am using aim to analyze charges of atoms in unit cell. The system I
> am looking at is FeTe with formal charge 2+ for Fe and 2- for Te. The
> keyword in case.inaim I used is Surf, and below is the last several
> lines of output file case.outputaim for Fe.
>
> Error analysis, values in degrees
> RMS Angular Error          3.23050888 Sum of moduli     0.383514
> Gradient weighted Error    0.14598727 Rho weighted      0.153686
> Estimated Charge Error     0.00056477 Electrons (only a rough estimate!)
>
> Integrated interstial charges:
> :RHO from Cubic Spline    1.72204544
> :RHO from Parabolic       1.72204461
> :RHOINTE (Quadrature)     1.72204615 :VOLUME    92.472093
>
> :PARABOLIC  for IND-ATOM   1  Z= 26.0  CHARGE:  25.88405837   0.11594163
> :CUBESPLINE for IND-ATOM   1  Z= 26.0  CHARGE:  25.88405920   0.11594080
> :RHOTOT     for IND-ATOM   1  Z= 26.0  CHARGE:  25.88405992   0.11594008
>  total cputime:   1586.22000000000       Wall    1613.10326910019
>
> Does this result mean that the charge of Fe is 0.12? That is far from
> 2+. How do I deal with interstitial charges of 1.72? I saw an old
> message in the maillist stated that there should be no interstitial
> charge in aim analysis. I am new to this aim, so any suggests are
> welcome. Thanks in advance!
>
> Best,
> Hefei
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-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu 1-847-491-3996
"Research is to see what everybody else has seen, and to think what
nobody else has thought"
Albert Szent-Gyorgi