Re: [Wien] How to simulate the ionic state of a compound?

[Abderrahmane Reggad]

Thank you Pieper and Luania for the deep explanations

Now the picture is very clear to me. Before i didn't know how does a dft
code work and somestime I have ambiguities between what magnetudes can we
manage in a dft code (wien2k) and those got from results of calculation.

Thank you again Luania for the articles

Best regards

2017-08-24 1:23 GMT+01:00 Abderrahmane Reggad :

> Thank you for all for the rich discussion
>
> If I introduce the Ni atom and I change the Z number to 27 or 26 it still
> nickel because the atom is ont only Z and I change Z the number of neutrons
> and protons still inchanged.As I mentionned when I have changed Z I have
> observed that the total energy changes.
>
> An other question: We suppose that the ionic state of NiO is a result from
> the electron density , can we force this ionic state to be Ni+3S-3 and it's
> yes how?
>
> Best regards
>
>
>
> 2017-08-24 0:43 GMT+01:00 Abderrahmane Reggad :
>
>> Hello
>>
>> The reason for my question is that I don't how does a DFT code work and I
>> want to know if the ionic state is a result or an assumption.
>>
>> Thank you for contribution to clarify the picture.
>>
>> Best regards
>>
>
>
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Re: [Wien] How to simulate the ionic state of a compound?

[Víctor Luaña Cabal]

On Thu, Aug 24, 2017 at 12:43:45AM +0100, Abderrahmane Reggad wrote:
> The reason for my question is that I don't how does a DFT code work and I
> want to know if the ionic state is a result or an assumption.

Abderrahmane,

In a wien2k calculation you provide the number of electrons assigned
to the core and to the valence regions of each chemical species in your
system.  However that is defining a population in orbital space. If the
calculations proceeds appropiatelryi (convergence of results, convergence
o basis set [k space], etc). The final distribution of the electrons
should not be determined by your assumptions, so obtaining an ionic,
covalent, metallic, magnetic, etc result should be a consecuence and
not an assumption. However, you must examine the correctness of the
calculation performing the analysis that is described in wien2k user
guide (muffin tin radius, k vectors, ...)

The analysis of the wien2k wavefunction and density can produce the
approximate picture of a very ionic system (NaCl and MgO, for instance),
a mostly covalent crystal (diamond and graphite, for instance), a
metallic one (alkali metals), and so on.


You can check all those examples in (sorry to describe my own
publications, but those are things that I know quite well ;-) )

* Ions in crystals: The topology of the electron density in ionic
  materials. II. The cubic alkali halide perovskites
  V Luaña, A Costales, AM Pendás
  Physical Review B 55 (7), 4285

* A classification of covalent, ionic, and metallic solids based on
  the electron density
  P Mori-Sánchez, AM Pendás, V Luaña
  Journal of the American Chemical Society 124 (49), 14721-14723

* Non-nuclear maxima of the electron density on alkaline metals
  V Luaña, P Mori-Sánchez, A Costales, MA Blanco, AM Pendás
  The Journal of chemical physics 119 (12), 6341-6350

* Topological characterization of the electron density laplacian in
  crystals. The case of the group IV elements
  A Otero-de-la-Roza, V Luaña
  Journal of Chemical Theory and Computation 6 (12), 3761-3779

* Ions in Crystals: The Topology of the Electron Density in Ionic
  Materials. 4. The Danburite (CaB2Si2O8) Case and the Occurrence of
  Oxide− Oxide Bond Paths in Crystals
  V Luana, A Costales, P Mori-Sanchez, AM Pendás
  The Journal of Physical Chemistry B 107 (21), 4912-4921


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Re: [Wien] How to simulate the ionic state of a compound?

[pieper]

High, Abderrahmane,


If I introduce the Ni atom and I change the Z number to 27 or 26 it
still nickel because the atom is ont only Z and I change Z the number
of neutrons and protons still inchanged.


NO! Z is the NUCLEAR charge. It sets the number of electrons 
automatically. If you change that you have another element! Try it by 
entering only the chemical symbol (e.g. Ni) in the corresponding field 
of the w2web struct editor. Leave the field Z empty. Press 'save and 
continue editing'. It will have filled in the correct Z automatically. 
One can circumvent this automatism, but it only makes sense if you know 
what you do. As I said before: find out yourself, start with a text book 
and the UG. You might learn enough in the process to know what you are 
doing.



An other question: We suppose that the ionic state of NiO is a result
from the electron density , can we force this ionic state to be
Ni+3S-3 and it's yes how?


Once again: You want to create some charge distribution of your own 
design where atom A lost electrons from and atom B caught them in what 
you decide is their own shell.


This is NOT what DFT or Wien2k does!

DFT gives you a (usually very good) approximation of where the electrons 
actually are in space. This may (in ionic crystals) or may not (with 
covalent or metallic bonds) agree more or less with your ideas.


Note that the agreement depends not only on the charge distribution 
itself! It heavily depends on how you decide by your experimental and/or 
computational methods which electron belongs where. Thats where the 
different definitions of charges Prof. Marks pointed out come from.


And try to get your hands on a good text book on solid state physics. It 
will help you far more than anyone in this mailing list can in his/her 
free time.


Best regards

Martin Pieper

---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564


Am 24.08.2017 02:23, schrieb Abderrahmane Reggad:

Thank you for all for the rich discussion

If I introduce the Ni atom and I change the Z number to 27 or 26 it
still nickel because the atom is ont only Z and I change Z the number
of neutrons and protons still inchanged.As I mentionned when I have
changed Z I have observed that the total energy changes.

An other question: We suppose that the ionic state of NiO is a result
from the electron density , can we force this ionic state to be
Ni+3S-3 and it's yes how?

Best regards

2017-08-24 0:43 GMT+01:00 Abderrahmane Reggad :


Hello

The reason for my question is that I don't how does a DFT code work
and I want to know if the ionic state is a result or an assumption.

Thank you for contribution to clarify the picture.

Best regards

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Re: [Wien] How to simulate the ionic state of a compound?

[Abderrahmane Reggad]

Thank you for all for the rich discussion

If I introduce the Ni atom and I change the Z number to 27 or 26 it still
nickel because the atom is ont only Z and I change Z the number of neutrons
and protons still inchanged.As I mentionned when I have changed Z I have
observed that the total energy changes.

An other question: We suppose that the ionic state of NiO is a result from
the electron density , can we force this ionic state to be Ni+3S-3 and it's
yes how?

Best regards



2017-08-24 0:43 GMT+01:00 Abderrahmane Reggad :

> Hello
>
> The reason for my question is that I don't how does a DFT code work and I
> want to know if the ionic state is a result or an assumption.
>
> Thank you for contribution to clarify the picture.
>
> Best regards
>
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http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
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Re: [Wien] How to simulate the ionic state of a compound?

[Abderrahmane Reggad]

Hello

The reason for my question is that I don't how does a DFT code work and I
want to know if the ionic state is a result or an assumption.

Thank you for contribution to clarify the picture.

Best regards
___
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Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:  
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Re: [Wien] How to simulate the ionic state of a compound?

[Laurence Marks]

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:

1) Bader charge: a measure of the ionicity.
2) Valence charge, as normally used this is the charge measured in an
electrochemical experiment. This corresponds to a purely ionic model.
3) Spectroscopies charge, what is measured using XPS and many other
Spectroscopies, and is close to the bond valence sum.
4) Born charge, the dynamic charge, for instance the effective charge of a
moving atom that one can get from a Berry phase calculation.

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).

---
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
http://www.numis.northwestern.edu
Corrosion in 4D http://MURI4D.numis.northwestern.edu
Partner of the CFW 100% gender equity project, www.cfw.org/100-percent
Co-Editor, Acta Cryst A


On Aug 23, 2017 06:58, "pieper"  wrote:

> Not knowing what your average Fe knows I still would guess it probably
> doesn't. Maybe thats why nothing else changes when you relabel atoms in
> xcrysden. However, upon adding two protons (and some neutrons) in
> Wien2k, Fe seems to know it became Ni - we learned from the initial
> question that it says so through ETOT. ;-)
>
> Best regards,
>
> Martin Pieper
>
> ---
> Dr. Martin Pieper
> Karl-Franzens University
> Institute of Physics
> Universitätsplatz 5
> A-8010 Graz
> Austria
> Tel.: +43-(0)316-380-8564
>
>
> Am 23.08.2017 11:16, schrieb Fecher, Gerhard:
> > Funny discussion,
> > I wonder wether iron (Z=26) knows that it is Nickel just if one gives
> > it a new name ?
> >
> >
> > Ciao
> > Gerhard
> >
> > DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
> > "I think the problem, to be quite honest with you,
> > is that you have never actually known what the question is."
> >
> > 
> > Dr. Gerhard H. Fecher
> > Institut of Inorganic and Analytical Chemistry
> > Johannes Gutenberg - University
> > 55099 Mainz
> > and
> > Max Planck Institute for Chemical Physics of Solids
> > 01187 Dresden
> > 
> > Von: Wien [wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von
> > Víctor Luaña Cabal [vic...@fluor.quimica.uniovi.es]
> > Gesendet: Mittwoch, 23. August 2017 00:33
> > An: A Mailing list for WIEN2k users
> > Cc: Victor Luaña
> > Betreff: Re: [Wien] How to simulate the ionic state of a compound?
> >
> > On Tue, Aug 22, 2017 at 11:41:53PM +0200, pieper wrote:
> >> my response to Abderrahmane Reggad appears perhaps a little harsh. It
> >> was not meant that way. I wanted to emphasize that in my view the idea
> >> of telling Wien2k (or any other DFT program) its result (where the
> >> electrons are) and to simulate properties from there is completely
> >> backwards.
> >
> > Martin,
> >
> > It was not harsh at all in my perception, but I canot say what
> > Abderrahmane thought about your words.
> >
> > I perceived as a normal exchange of ideas in a subject that I love.
> >
> > I agree that using a questionable populaton technique to obtain a
> > number
> > of electrons associated to an ion from a expensive DFT calculation
> > is not neccesarily a good idea. Providing a number to say this is a
> > Ni(+1.98) O(-2.02) crystal should not be the main result from a good
> > article. However, a good physically based theory of chemical bonding in
> > molecules, solids and clusters provides far more that that.
> >
> > Let me be very particular in describing QTAIM (quantum theory of atoms
> > in molecules, aka Richard F. W. Bader et al work) as a beautiful and
> > well founded physical teory on chemical bonding.
> >
> > Bader's QTAIM can be used to partition every property into
> > contributions
> > of a particular atom or functional group.
> >
> > Then you can find an explanation why many perovskite oxides, for
> > instance, have a very similar bulk modulus, and the explanation comes
> > from the fact that the oxide is the major contribution, and that
> > contribution is common to the incumbent crystals.
> >
> >> This is, however, what I wanted to point out: DFT (or Wien2k) tells
> >> you
> >> where the electrons are. Thats its central result. It does not make
> >> any
> >> sense (to me) to use a DFT program to - as A. Reggad put it -
> >> "simulate
> >> the NiO compound in its ionic state". If NiO would be a ionic compound
> >> then DFT would (hopefully, when set up properly) calculate an electron
> >> density with a lot of weight at O and a lot less at Ni as a RESULT.
> >> The
> >> simulation of any property one wishes to study can proceed from there.
> >
> > I agree, of course. That should be the spirit of an ab initio
> > 

Re: [Wien] How to simulate the ionic state of a compound?

[pieper]

Not knowing what your average Fe knows I still would guess it probably 
doesn't. Maybe thats why nothing else changes when you relabel atoms in 
xcrysden. However, upon adding two protons (and some neutrons) in 
Wien2k, Fe seems to know it became Ni - we learned from the initial 
question that it says so through ETOT. ;-)


Best regards,

Martin Pieper

---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564


Am 23.08.2017 11:16, schrieb Fecher, Gerhard:

Funny discussion,
I wonder wether iron (Z=26) knows that it is Nickel just if one gives
it a new name ?


Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."


Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
and
Max Planck Institute for Chemical Physics of Solids
01187 Dresden

Von: Wien [wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von
Víctor Luaña Cabal [vic...@fluor.quimica.uniovi.es]
Gesendet: Mittwoch, 23. August 2017 00:33
An: A Mailing list for WIEN2k users
Cc: Victor Luaña
Betreff: Re: [Wien] How to simulate the ionic state of a compound?

On Tue, Aug 22, 2017 at 11:41:53PM +0200, pieper wrote:

my response to Abderrahmane Reggad appears perhaps a little harsh. It
was not meant that way. I wanted to emphasize that in my view the idea
of telling Wien2k (or any other DFT program) its result (where the
electrons are) and to simulate properties from there is completely
backwards.


Martin,

It was not harsh at all in my perception, but I canot say what
Abderrahmane thought about your words.

I perceived as a normal exchange of ideas in a subject that I love.

I agree that using a questionable populaton technique to obtain a 
number

of electrons associated to an ion from a expensive DFT calculation
is not neccesarily a good idea. Providing a number to say this is a
Ni(+1.98) O(-2.02) crystal should not be the main result from a good
article. However, a good physically based theory of chemical bonding in
molecules, solids and clusters provides far more that that.

Let me be very particular in describing QTAIM (quantum theory of atoms
in molecules, aka Richard F. W. Bader et al work) as a beautiful and
well founded physical teory on chemical bonding.

Bader's QTAIM can be used to partition every property into 
contributions

of a particular atom or functional group.

Then you can find an explanation why many perovskite oxides, for
instance, have a very similar bulk modulus, and the explanation comes
from the fact that the oxide is the major contribution, and that
contribution is common to the incumbent crystals.

This is, however, what I wanted to point out: DFT (or Wien2k) tells 
you
where the electrons are. Thats its central result. It does not make 
any
sense (to me) to use a DFT program to - as A. Reggad put it - 
"simulate

the NiO compound in its ionic state". If NiO would be a ionic compound
then DFT would (hopefully, when set up properly) calculate an electron
density with a lot of weight at O and a lot less at Ni as a RESULT. 
The

simulation of any property one wishes to study can proceed from there.


I agree, of course. That should be the spirit of an ab initio 
calculation.

However, DFT sometimes separates from the ab initio family when the xc
functional is chosen not because of its properties or for exploring the
sensibility of the predictions to the functional but because a spurious
predictive agreement to whatever 'experiment'.

I believe finding explanations to peculiar facts is the real motive
of computational research, at least until the point is achieved at
which theoretical calculations become competitive with experimental
measurements in terms of precision, exactitude and cost.


And if the electron density of NiO does not really resemble the ionic
picture, why use the ionic model to simulate things?


Yes, but having a predictive measurement of the ionicity lets you
examine how ionicity depends on thermodynamic conditions: is the effect
of pressure more important than the effect of temperature or pH ... on
a geological scale?

*Chemical bonding* can be at the core of geophysics, research on
materials, ... and many more fields. However, I'm a peculiar chemist 
and

I love Physical Review since I was working on my phd thesis, long ago.

Best regards from sunny north Spain,
Víctor
--
.  ."Half of the US people use twitter to form its opinion and 
half
   / `' \   also elect the US president. I only hope they are not the 
same

  /(o)(o)\  half". --From a sentence by Gore Vidal
 /`. \/ .'\
/   '`'`   \ "[Technocrats, academics and journalists] are often 
motivated

|  \'`'`/  | by hope while the public at large tends to be more focused

Re: [Wien] How to simulate the ionic state of a compound?

[Fecher, Gerhard]

Funny discussion,
I wonder wether iron (Z=26) knows that it is Nickel just if one gives it a new 
name ?


Ciao
Gerhard

DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
"I think the problem, to be quite honest with you,
is that you have never actually known what the question is."


Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
and
Max Planck Institute for Chemical Physics of Solids
01187 Dresden

Von: Wien [wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von Víctor Luaña 
Cabal [vic...@fluor.quimica.uniovi.es]
Gesendet: Mittwoch, 23. August 2017 00:33
An: A Mailing list for WIEN2k users
Cc: Victor Luaña
Betreff: Re: [Wien] How to simulate the ionic state of a compound?

On Tue, Aug 22, 2017 at 11:41:53PM +0200, pieper wrote:
> my response to Abderrahmane Reggad appears perhaps a little harsh. It
> was not meant that way. I wanted to emphasize that in my view the idea
> of telling Wien2k (or any other DFT program) its result (where the
> electrons are) and to simulate properties from there is completely
> backwards.

Martin,

It was not harsh at all in my perception, but I canot say what
Abderrahmane thought about your words.

I perceived as a normal exchange of ideas in a subject that I love.

I agree that using a questionable populaton technique to obtain a number
of electrons associated to an ion from a expensive DFT calculation
is not neccesarily a good idea. Providing a number to say this is a
Ni(+1.98) O(-2.02) crystal should not be the main result from a good
article. However, a good physically based theory of chemical bonding in
molecules, solids and clusters provides far more that that.

Let me be very particular in describing QTAIM (quantum theory of atoms
in molecules, aka Richard F. W. Bader et al work) as a beautiful and
well founded physical teory on chemical bonding.

Bader's QTAIM can be used to partition every property into contributions
of a particular atom or functional group.

Then you can find an explanation why many perovskite oxides, for
instance, have a very similar bulk modulus, and the explanation comes
from the fact that the oxide is the major contribution, and that
contribution is common to the incumbent crystals.

> This is, however, what I wanted to point out: DFT (or Wien2k) tells you
> where the electrons are. Thats its central result. It does not make any
> sense (to me) to use a DFT program to - as A. Reggad put it - "simulate
> the NiO compound in its ionic state". If NiO would be a ionic compound
> then DFT would (hopefully, when set up properly) calculate an electron
> density with a lot of weight at O and a lot less at Ni as a RESULT. The
> simulation of any property one wishes to study can proceed from there.

I agree, of course. That should be the spirit of an ab initio calculation.
However, DFT sometimes separates from the ab initio family when the xc
functional is chosen not because of its properties or for exploring the
sensibility of the predictions to the functional but because a spurious
predictive agreement to whatever 'experiment'.

I believe finding explanations to peculiar facts is the real motive
of computational research, at least until the point is achieved at
which theoretical calculations become competitive with experimental
measurements in terms of precision, exactitude and cost.

> And if the electron density of NiO does not really resemble the ionic
> picture, why use the ionic model to simulate things?

Yes, but having a predictive measurement of the ionicity lets you
examine how ionicity depends on thermodynamic conditions: is the effect
of pressure more important than the effect of temperature or pH ... on
a geological scale?

*Chemical bonding* can be at the core of geophysics, research on
materials, ... and many more fields. However, I'm a peculiar chemist and
I love Physical Review since I was working on my phd thesis, long ago.

Best regards from sunny north Spain,
Víctor
--
.  ."Half of the US people use twitter to form its opinion and half
   / `' \   also elect the US president. I only hope they are not the same
  /(o)(o)\  half". --From a sentence by Gore Vidal
 /`. \/ .'\
/   '`'`   \ "[Technocrats, academics and journalists] are often motivated
|  \'`'`/  | by hope while the public at large tends to be more focused
|  |'`'`|  | on fear." -- Russell Mead (The Washington Post, 2017)
 \/`'`'`'\/
==(((==)))===+===
! Dr.Víctor Luaña, in silico chemist & prof. !
! Departamento de Química Física y Analítica !
! Universidad de Oviedo, 33006-Oviedo, Spain !
! e-mail:    !
! phone: +34-985-103491  fax: +34-985-103125 !
++
 GroupPage: 
 Articles:  

Re: [Wien] How to simulate the ionic state of a compound?

[Víctor Luaña Cabal]

On Tue, Aug 22, 2017 at 11:41:53PM +0200, pieper wrote:
> my response to Abderrahmane Reggad appears perhaps a little harsh. It  
> was not meant that way. I wanted to emphasize that in my view the idea  
> of telling Wien2k (or any other DFT program) its result (where the  
> electrons are) and to simulate properties from there is completely  
> backwards.

Martin,

It was not harsh at all in my perception, but I canot say what
Abderrahmane thought about your words.

I perceived as a normal exchange of ideas in a subject that I love.

I agree that using a questionable populaton technique to obtain a number
of electrons associated to an ion from a expensive DFT calculation
is not neccesarily a good idea. Providing a number to say this is a
Ni(+1.98) O(-2.02) crystal should not be the main result from a good
article. However, a good physically based theory of chemical bonding in
molecules, solids and clusters provides far more that that.

Let me be very particular in describing QTAIM (quantum theory of atoms
in molecules, aka Richard F. W. Bader et al work) as a beautiful and
well founded physical teory on chemical bonding.

Bader's QTAIM can be used to partition every property into contributions
of a particular atom or functional group.

Then you can find an explanation why many perovskite oxides, for
instance, have a very similar bulk modulus, and the explanation comes
from the fact that the oxide is the major contribution, and that
contribution is common to the incumbent crystals.

> This is, however, what I wanted to point out: DFT (or Wien2k) tells you  
> where the electrons are. Thats its central result. It does not make any  
> sense (to me) to use a DFT program to - as A. Reggad put it - "simulate  
> the NiO compound in its ionic state". If NiO would be a ionic compound  
> then DFT would (hopefully, when set up properly) calculate an electron  
> density with a lot of weight at O and a lot less at Ni as a RESULT. The  
> simulation of any property one wishes to study can proceed from there.

I agree, of course. That should be the spirit of an ab initio calculation.
However, DFT sometimes separates from the ab initio family when the xc
functional is chosen not because of its properties or for exploring the
sensibility of the predictions to the functional but because a spurious
predictive agreement to whatever 'experiment'.

I believe finding explanations to peculiar facts is the real motive
of computational research, at least until the point is achieved at
which theoretical calculations become competitive with experimental
measurements in terms of precision, exactitude and cost.

> And if the electron density of NiO does not really resemble the ionic  
> picture, why use the ionic model to simulate things?

Yes, but having a predictive measurement of the ionicity lets you
examine how ionicity depends on thermodynamic conditions: is the effect
of pressure more important than the effect of temperature or pH ... on
a geological scale?

*Chemical bonding* can be at the core of geophysics, research on
materials, ... and many more fields. However, I'm a peculiar chemist and
I love Physical Review since I was working on my phd thesis, long ago.

Best regards from sunny north Spain,
Víctor
--
.  ."Half of the US people use twitter to form its opinion and half
   / `' \   also elect the US president. I only hope they are not the same
  /(o)(o)\  half". --From a sentence by Gore Vidal
 /`. \/ .'\
/   '`'`   \ "[Technocrats, academics and journalists] are often motivated
|  \'`'`/  | by hope while the public at large tends to be more focused
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Re: [Wien] How to simulate the ionic state of a compound?

[pieper]

High Victor,

my response to Abderrahmane Reggad appears perhaps a little harsh. It 
was not meant that way. I wanted to emphasize that in my view the idea 
of telling Wien2k (or any other DFT program) its result (where the 
electrons are) and to simulate properties from there is completely 
backwards.


Of course I agree with you that the electron density of a solid is a 
real observable - even in the XXI century. Quantum mechanics was 
invented to calculate such properties and the density is, after all, the 
D in DFT. I also agree that there are any number of solids where a ionic 
description makes perfect sense. I never tried but I am very confident 
that the ionic nature of alkali halides will be evident from the result 
of a DFT calculation.


This is, however, what I wanted to point out: DFT (or Wien2k) tells you 
where the electrons are. Thats its central result. It does not make any 
sense (to me) to use a DFT program to - as A. Reggad put it - "simulate 
the NiO compound in its ionic state". If NiO would be a ionic compound 
then DFT would (hopefully, when set up properly) calculate an electron 
density with a lot of weight at O and a lot less at Ni as a RESULT. The 
simulation of any property one wishes to study can proceed from there.


And if the electron density of NiO does not really resemble the ionic 
picture, why use the ionic model to simulate things?


Best regards,

Martin


---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564


Am 22.08.2017 20:45, schrieb Víctor Luaña Cabal:

On Tue, Aug 22, 2017 at 07:00:07PM +0200, pieper wrote:

DFT in general and Wien2k especially are there to tell you with
remarkably high precision what the charge distribution in a given
structure actually looks like. Thats FAR better than any hand-waving 
Ni
is 2+, O 2-. If you don't like what DFT tells you and want to draw 
some

fictitious ionic representation of NiO, take xcrysden, plot the
structure, and add labels saying that the (maybe) red circles are Ni2+
and the (maybe) blue circles are O2-.

It should be obvious to you from your lectures and readings on solid
state physics that the total energy depends on Z. If you change the
nuclear charge Z you change the element at that position. One can 
adjust
the number of electrons and their starting distribution in Wien2k, but 
I

plainly won't tell you how. You will learn much more if you find out
yourself - start with the User Guide and a solid state physics text
book.



martin,

Nothing against your description and I agree basically with
everything. However, the electron density (\rho) of a molecule or
solid is a real and mensurable property that exists in 3D real position
space, so the topology of \rho can be examined properly: that's Bader
topological analysis. A mostly physical and matematical description of
molecules and solids. Similarly, there are other scalar properties that
are physically well defined.

By Bader topological analysis we know that some systems are truly
ionic in nature, like alkali halides or simple oxides, but that is not
any surprise and crystallographers have used that since Laue and the
Braggs. Other materials are more interesting, however, and pressure
(thermodynamics, in general) modifies behavior of BP from being mostly
boron phosphide to phosporus boride, including a pressure range in 
which
electrons behave as independent chemical items and we have an 
electride.

[Phys. Rev. B  63 (2001) 125103, Polarity inversion in the electron
density of BP crystal, Paula Mori-Sánchez et al.]

In molecules, for instance, we have the Electrostatic potential as a 
well

defined scalar property. In some ways it brings us from XX century
(the century of quantum mechanics and electron density, quite complex
due to the effect of correlation and basis sets) to XIX century with
Maxwell and Faraday (positive and negative charge distributions are
what we need to know).

Unfortunately, in solids there is a real indetermination with the zero 
of

the EP, that it is basically arbitrary, as much as I know.


Nice subject, if you let me tell, by the way. Best regards,
   Víctor Luaña
--
.  ."Half of the US people use twitter to form its opinion and 
half
   / `' \   also elect the US president. I only hope they are not the 
same

  /(o)(o)\  half". --From a sentence by Gore Vidal
 /`. \/ .'\
/   '`'`   \ "[Technocrats, academics and journalists} are often 
motivated

|  \'`'`/  | by hope while the public at large tends to be more focused
|  |'`'`|  | on fear." -- Russell Mead (The Washington Post, 2017)
 \/`'`'`'\/
==(((==)))===+===
! Dr.Víctor Luaña, in silico chemist & prof. !
! Departamento de Química Física y Analítica !
! Universidad de Oviedo, 33006-Oviedo, Spain !
! e-mail:    !
! phone: +34-985-103491  fax: +34-985-103125 !

Re: [Wien] How to simulate the ionic state of a compound?

[pieper]

DFT in general and Wien2k especially are there to tell you with 
remarkably high precision what the charge distribution in a given 
structure actually looks like. Thats FAR better than any hand-waving Ni 
is 2+, O 2-. If you don't like what DFT tells you and want to draw some 
fictitious ionic representation of NiO, take xcrysden, plot the 
structure, and add labels saying that the (maybe) red circles are Ni2+ 
and the (maybe) blue circles are O2-.


It should be obvious to you from your lectures and readings on solid 
state physics that the total energy depends on Z. If you change the 
nuclear charge Z you change the element at that position. One can adjust 
the number of electrons and their starting distribution in Wien2k, but I 
plainly won't tell you how. You will learn much more if you find out 
yourself - start with the User Guide and a solid state physics text 
book.




---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564


Am 22.08.2017 12:19, schrieb Abderrahmane Reggad:

Dear wien users

I want to simulate the NiO compound in its ionic state. We know that
the Ni and O atoms have in their neutral state the atomic numbers 28
and 8 respectively.

Now, if we want to study the ionic state of the compound Ni+2O-2,
should we modify the atomic numbers to Z=26 for Ni and Z=10 for O, or
the wien2k code do the operation instead of us?

NB: When I change the Z number for Ni atom I found a change in the
energy value.

Best regards
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[Wien] How to simulate the ionic state of a compound?

[Abderrahmane Reggad]

Dear wien users

I want to simulate the NiO compound in its ionic state. We know that the Ni
and O atoms have in their neutral state the atomic numbers 28 and 8
respectively.

Now, if we want to study the ionic state of the compound Ni+2O-2, should we
modify the atomic numbers to Z=26 for Ni and Z=10 for O, or the wien2k code
do the operation instead of us?

NB: When I change the Z number for Ni atom I found a change in the energy
value.


Best regards
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