[Wien] Questions about the difference charge density in the Ti core

[Peter Blaha]

Hi,

Please read the rest of the article. There is NO indication of a Ti4+, 
because this is not a very ionic compound. What is evident, is a strong 
anisotropy of the occupied 3d electrons, both on Co and Ti.

What you seem to call "core" region, comes from the 3d electrons, whose 
maximum is really quite localized.

Remember, this is a "chemical valence" (in a purely ionic picture), a 
"formal" quantitiy.

In addition: If Ti is 4+, where would these electrons go ? Sb is in 
group V, so can at most take 3 electrons, thus in your ionic picture you 
get:  Ti4+ Co-1 Sb-3 .   This can't be correct and while it is 
impossible to give quantitative numbers of a charge transfer, there is 
some indication (Table II) that Co takes some electrons from Ti (the Co 
3d states are lower in energy than Ti3d/4s), while Sb is slightly 
negative (Bader) or even positive (QTL). As is evident from the 
difference density, there is a huge region of nearly zero 
difference-density. These interstitial charge, however, cannot be easily 
and uniquely attributed to specific atoms and can stem from all 
delocalized wave functions (Ti-4s, Co-4s, Sb-5p - see Table I abould 
"localized 3d" and delocalized sp electrons).

Am 02.05.2020 um 07:45 schrieb Ding Peng:
> Dear Wien2k experts,
> 
> I'm reading the latest publication for Wien2k (P. Blaha, K.Schwarz, F. Tran, R. Laskowski, G.K.H. Madsen and L.D. Marks, J. Chem. Phys. 152, 074101 (2020)) and confused about the figure showing the difference charge density of TiCoSb (Figure 9 in the paper). I noticed that the core charge densities for Ti and Co are very positive and the ones for Sb are very negative. To my best knowledge, Ti in TiCoSb is thought to have the chemical valence of +4, which means it tends to lose the electrons. However, this looks to contradict to the this graph, in which the difference charge densities in Ti are positive. So can someone explain why the difference charge densities in Ti core are very positive?
> 
> Sorry for asking this question that may look stupid.
> 
> Many thanks,
> Ding
> 
> 
> 
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-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
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