[Wien] Degree of bond ionicity

[Antoine Villesuzanne]

Although not uniquely defined, the degree of ionicity can be inferred from 
several quantities extracted from Wien2k calculations :
- Projected density of states (Al contribution to N-character bands, for 
example, should be the smallest for a very ionic bonding)
- Atomic net charge : poorly reliable when extracted from integration in 
atomic spheres. Much more reliable when extracted from AIM theory (aim 
program in Wien2k), in which the full electron density is unambiguously 
divided in atomic "basins". However, keep in mind that ionicity or partial 
charges are not observables, and any "degree of ionicity" is slave to a 
model, even in AIM theory.

The Electron Localization Function (not implemented in Wien2k) would 
indicate the departure from covalent bonding in series of compounds.

Antoine Villesuzanne
ICMCB-CNRS
87, Av. Dr. A. Schweitzer
33608 Pessac Cedex
Tél. 33 (0) 540008459
Fax 33 (0) 540008373
----- Original Message ----- 
From: "Pedro M. F. J. Costa" <pmfjc2 at cam.ac.uk>
To: <wien at zeus.theochem.tuwien.ac.at>
Sent: Wednesday, July 05, 2006 3:46 AM
Subject: [Wien] Degree of bond ionicity


> Dear all,
>
> Having read the manual, FAQs and the mailing list QandA, I find myself 
> with
> a question that has not yet been approached.
>
> I have been studying III/V systems such as AlN and GaN. At this stage, I
> would like to enquire whether it is possible with Wien2k to make an
> estimation of the degree of ionicity of a bound. From the distribution of
> valence-electron charge density I can infer how the maximum of charge
> density (and therefore degree of ionicity) is shifted simply by changing
> the cations in a series of nitride compounds. I suppose that one could 
> draw
> trend lines between a series of substances but in this case what method 
> can
> I use to extract some reliable figures of ionicity degree?
>
> Yours,
>
> Pedro
> -- 
> **************************************************************************
> Pedro Miguel F. J. Costa
>
> Department of Materials Science and Metallurgy
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>
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