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

[Ding Peng]

Dear Dr Fabien Tran,

Thanks for your reply. Your explanation is very clear and helpful!

Ding

On Sat, 2 May 2020 at 18:49, Tran, Fabien <fabien.tran at tuwien.ac.at> wrote:

> Hi,
>
> The valence orbitals can also extend in the region (very) close to the
> nucleus.
> An example is given in Fig. 4 in our recent paper (
> https://arxiv.org/abs/2004.04543),
> which shows that most of the 3d electrons of Fe is within 1 bohr from the
> nucleus.
>
> Another thing: Sometimes a 2D plot can be misleading and lead to a wrong
> impression.
> In this (110) plane in Fig. 9 that you mentioned, there are indeed two big
> purple lobs,
> but this may be different in another plane. As Peter B. mentioned, Ti
> looses electrons
> compared to the free atom (see Table II).
>
> FT
>
> ________________________________________
> From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of Ding
> Peng <ding.peng at monash.edu>
> Sent: Saturday, May 2, 2020 11:15 AM
> To: A Mailing list for WIEN2k users
> Subject: Re: [Wien] Questions about the difference charge density in the
> Ti core
>
> Dear Prof Peter Blaha,
>
> Many thanks for your feedback. I'm very grateful to this.
>
> I'm sorry for my bad description of the "core" region. The "core" region
> that mentioned in my last email is the "round region" at the centre of Ti
> atomic site , which is most likely to be contributed by the core states
> (1s, 2s, 2p, etc.) and the semicore states (3s, 3p) of Ti. If the
> difference charge density is defined as the charge density of the solid
> minus the superposed charge densities, the centre region would be about
> zero since the core states haven't participate in the bonding (please
> correct me if I'm wrong). But what I can see from the graph is very deep
> purple-coloured region at the centre of the Ti site, which suggests a dense
> accumulation of electrons at the Ti site. So could I ask why the difference
> charge densities in this "round region" is very positive?
>
> Many thanks,
> Ding
>
>
>
> > On 2 May 2020, at 3:48 pm, Peter Blaha <pblaha at theochem.tuwien.ac.at>
> wrote:
> >
> > 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
> > +43-1-5880115671
> > _______________________________________________
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