<div dir="auto">I am not sure where this discussion is wandering. There is one general point of some importance: the " Charge" or "Ionic State" is not an absolute number, it changes with the property/experiment:<div dir="auto"><br></div><div dir="auto">1) Bader charge: a measure of the ionicity.</div><div dir="auto">2) Valence charge, as normally used this is the charge measured in an electrochemical experiment. This corresponds to a purely ionic model.</div><div dir="auto">3) Spectroscopies charge, what is measured using XPS and many other Spectroscopies, and is close to the bond valence sum.</div><div dir="auto">4) Born charge, the dynamic charge, for instance the effective charge of a moving atom that one can get from a Berry phase calculation.</div><div dir="auto"><br></div><div dir="auto">1)-4) are all different, and if you use them inappropriately GIGO. For instance, there is the infamous polar catastrophy at surfaces/interfaces that arises when people nievely use 2).<br><br><div data-smartmail="gmail_signature" dir="auto">---<br>Professor Laurence Marks<br>"Research is to see what everybody else has seen, and to think what nobody else has thought", Albert Szent-Gyorgi<br><a href="http://www.numis.northwestern.edu">http://www.numis.northwestern.edu</a><br>Corrosion in 4D <a href="http://MURI4D.numis.northwestern.edu">http://MURI4D.numis.northwestern.edu</a><br>Partner of the CFW 100% gender equity project, <a href="http://www.cfw.org/100-percent">www.cfw.org/100-percent</a><br>Co-Editor, Acta Cryst A<br>    </div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Aug 23, 2017 06:58, "pieper" <<a href="mailto:pieper@ifp.tuwien.ac.at">pieper@ifp.tuwien.ac.at</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Not knowing what your average Fe knows I still would guess it probably<br>
doesn't. Maybe thats why nothing else changes when you relabel atoms in<br>
xcrysden. However, upon adding two protons (and some neutrons) in<br>
Wien2k, Fe seems to know it became Ni - we learned from the initial<br>
question that it says so through ETOT. ;-)<br>
<br>
Best regards,<br>
<br>
Martin Pieper<br>
<br>
---<br>
Dr. Martin Pieper<br>
Karl-Franzens University<br>
Institute of Physics<br>
Universitätsplatz 5<br>
A-8010 Graz<br>
Austria<br>
Tel.: +43-(0)316-380-8564<br>
<br>
<br>
Am 23.08.2017 11:16, schrieb Fecher, Gerhard:<br>
> Funny discussion,<br>
> I wonder wether iron (Z=26) knows that it is Nickel just if one gives<br>
> it a new name ?<br>
><br>
><br>
> Ciao<br>
> Gerhard<br>
><br>
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:<br>
> "I think the problem, to be quite honest with you,<br>
> is that you have never actually known what the question is."<br>
><br>
> ==============================<wbr>======<br>
> Dr. Gerhard H. Fecher<br>
> Institut of Inorganic and Analytical Chemistry<br>
> Johannes Gutenberg - University<br>
> 55099 Mainz<br>
> and<br>
> Max Planck Institute for Chemical Physics of Solids<br>
> 01187 Dresden<br>
> ______________________________<wbr>__________<br>
> Von: Wien [<a href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.<wbr>tuwien.ac.at</a>] im Auftrag von<br>
> Víctor Luaña Cabal [<a href="mailto:victor@fluor.quimica.uniovi.es">victor@fluor.quimica.uniovi.<wbr>es</a>]<br>
> Gesendet: Mittwoch, 23. August 2017 00:33<br>
> An: A Mailing list for WIEN2k users<br>
> Cc: Victor Luaña<br>
> Betreff: Re: [Wien] How to simulate the ionic state of a compound?<br>
><br>
> On Tue, Aug 22, 2017 at 11:41:53PM +0200, pieper wrote:<br>
>> my response to Abderrahmane Reggad appears perhaps a little harsh. It<br>
>> was not meant that way. I wanted to emphasize that in my view the idea<br>
>> of telling Wien2k (or any other DFT program) its result (where the<br>
>> electrons are) and to simulate properties from there is completely<br>
>> backwards.<br>
><br>
> Martin,<br>
><br>
> It was not harsh at all in my perception, but I canot say what<br>
> Abderrahmane thought about your words.<br>
><br>
> I perceived as a normal exchange of ideas in a subject that I love.<br>
><br>
> I agree that using a questionable populaton technique to obtain a<br>
> number<br>
> of electrons associated to an ion from a expensive DFT calculation<br>
> is not neccesarily a good idea. Providing a number to say this is a<br>
> Ni(+1.98) O(-2.02) crystal should not be the main result from a good<br>
> article. However, a good physically based theory of chemical bonding in<br>
> molecules, solids and clusters provides far more that that.<br>
><br>
> Let me be very particular in describing QTAIM (quantum theory of atoms<br>
> in molecules, aka Richard F. W. Bader et al work) as a beautiful and<br>
> well founded physical teory on chemical bonding.<br>
><br>
> Bader's QTAIM can be used to partition every property into<br>
> contributions<br>
> of a particular atom or functional group.<br>
><br>
> Then you can find an explanation why many perovskite oxides, for<br>
> instance, have a very similar bulk modulus, and the explanation comes<br>
> from the fact that the oxide is the major contribution, and that<br>
> contribution is common to the incumbent crystals.<br>
><br>
>> This is, however, what I wanted to point out: DFT (or Wien2k) tells<br>
>> you<br>
>> where the electrons are. Thats its central result. It does not make<br>
>> any<br>
>> sense (to me) to use a DFT program to - as A. Reggad put it -<br>
>> "simulate<br>
>> the NiO compound in its ionic state". If NiO would be a ionic compound<br>
>> then DFT would (hopefully, when set up properly) calculate an electron<br>
>> density with a lot of weight at O and a lot less at Ni as a RESULT.<br>
>> The<br>
>> simulation of any property one wishes to study can proceed from there.<br>
><br>
> I agree, of course. That should be the spirit of an ab initio<br>
> calculation.<br>
> However, DFT sometimes separates from the ab initio family when the xc<br>
> functional is chosen not because of its properties or for exploring the<br>
> sensibility of the predictions to the functional but because a spurious<br>
> predictive agreement to whatever 'experiment'.<br>
><br>
> I believe finding explanations to peculiar facts is the real motive<br>
> of computational research, at least until the point is achieved at<br>
> which theoretical calculations become competitive with experimental<br>
> measurements in terms of precision, exactitude and cost.<br>
><br>
>> And if the electron density of NiO does not really resemble the ionic<br>
>> picture, why use the ionic model to simulate things?<br>
><br>
> Yes, but having a predictive measurement of the ionicity lets you<br>
> examine how ionicity depends on thermodynamic conditions: is the effect<br>
> of pressure more important than the effect of temperature or pH ... on<br>
> a geological scale?<br>
><br>
> *Chemical bonding* can be at the core of geophysics, research on<br>
> materials, ... and many more fields. However, I'm a peculiar chemist<br>
> and<br>
> I love Physical Review since I was working on my phd thesis, long ago.<br>
><br>
> Best regards from sunny north Spain,<br>
>                                     Víctor<br>
> --<br>
>     .  .    "Half of the US people use twitter to form its opinion and<br>
> half<br>
>    / `' \   also elect the US president. I only hope they are not the<br>
> same<br>
>   /(o)(o)\  half". --From a sentence by Gore Vidal<br>
>  /`. \/ .'\<br>
> /   '`'`   \ "[Technocrats, academics and journalists] are often<br>
> motivated<br>
> |  \'`'`/  | by hope while the public at large tends to be more focused<br>
> |  |'`'`|  | on fear." -- Russell Mead (The Washington Post, 2017)<br>
>  \/`'`'`'\/<br>
> ==(((==)))====================<wbr>===============+==============<wbr>=============<br>
> ! Dr.Víctor Luaña, in silico chemist & prof. !<br>
> ! Departamento de Química Física y Analítica !<br>
> ! Universidad de Oviedo, 33006-Oviedo, Spain !<br>
> ! e-mail:  <<a href="mailto:victor@fluor.quimica.uniovi.es">victor@fluor.quimica.uniovi.<wbr>es</a>>  !<br>
> ! phone: +34-985-103491  fax: +34-985-103125 !<br>
> +-----------------------------<wbr>---------------+<br>
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