[Pw_forum] what's the unit of charge density

[vega lew]

Dear friend,

thank you for your help. your answer is quite useful for us.

>I am not aware of any tool in the distribution that can do overlap
>populations.

as far as I know, this function could be accomplished during Mulliken bond
population analysis in CASTEP.
I used to think this kind of analysis could help us to understand our
promble.

>Perhaps, instead of overlap population, you may plot the atomic
>projected-densities of states (using projwfc.x), and you can look how
>good is the PDOS "alignment" between the atoms in question ...
>Or you may plot the 2D contour plot of either charge density difference
>or integrated local density of states along the bond direction.

could you give me some more information about plotting the charge density
difference map.
which command in QE should be used for that plotting? And I also found 2D
contour is a little
hard for our problem, because our model is a slab geometry, and the atoms on
the surface goes
ups and downs. Thus, we can't  put all the atoms we are focus on in one 2D
map.

could you please tell me more about how to integrated lDoS along the bond
direction? Do you mean
I could plot the pDoS for certain atoms, and then integrate it to the HOMO?

thank you again for your kind help

best wishes,

vega

On Tue, Apr 14, 2009 at 6:15 PM, Tone Kokalj <tone.kokalj at ijs.si> wrote:

> On Sat, 2009-04-11 at 15:15 +0800, vega lew wrote:
> > Dear all
> >
> > I just ploted the 3D charge density using pp.x code.  And XCRYSDEN was
> > used for displaying the 3D isosurface of charge density. When I set
> > the isovalue for different number, such as 0.15 or less, I fould the
> > overlap of electron cloud is quite meanful for different systems of
> > distinct catalysis activities. I wonder what the unit of charge
> > density?
>
> xcrysden does not assume any units, and merely takes the values as
> stated in the file. The unit is therefore up to the creator of the XSF
> file.
>
> If the XSF file was produced by pp.x, then the unit of charge is
> electron/bohr^3.
>
>
> > and whether the absolute value of it could be directly comparable for
> > different systems ( same number of atoms, same element, only different
> > in geometry of the model)?
>
> Yes, because the unit is electron/bohr^3 (for pp.x).
>
> > By the way, is there a tutorial for population analysis? I wonder
> > where I could find the value of overap population for a pair of
> > atoms.
>
> The PWscf uses Lowdin population analysis that can be performed by
> projwfc.x. Note however the ingredients are lowdin oribtals, which are
> orthonormal, i.e.:
>
> LowdinOrb_\mu = \sum_\nu S_{\mu,\nu}^{1/2} AO_\nu,
>
> where S_{\mu,\nu}^{1/2} is the element of the square root inverse of the
> overlap matrix S of the atomic orbitals AO. Because lowdin orbitals are
> orthogonal there is no overlap between them ==> no overlap population!
>
> I am not aware of any tool in the distribution that can do overlap
> populations.
>
> Perhaps, instead of overlap population, you may plot the atomic
> projected-densities of states (using projwfc.x), and you can look how
> good is the PDOS "alignment" between the atoms in question ...
> Or you may plot the 2D contour plot of either charge density difference
> or integrated local density of states along the bond direction.
>
> Regards, Tone
>
> --
> Anton Kokalj
> J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
> (tel: +386-1-477-3523 // fax:+386-1-477-3822)
>
> Please, if possible, avoid sending me Word or PowerPoint attachments.
> See:  http://www.gnu.org/philosophy/no-word-attachments.html
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>



-- 
==================================================================================
Vega Lew ( weijia liu)
PH.D Candidate in Chemical Engineering
State Key Laboratory of Materials-oriented Chemical Engineering
College of Chemistry and Chemical Engineering
Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
******************************************************************************************************************
Email: vegalew at gmail.com
Office: Room A705, Technical Innovation Building, Xinmofan Road 5#, Nanjing,
Jiangsu, China
******************************************************************************************************************
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20090417/55b487cb/attachment.html>