[Wien] EELS of L3 Ti edge

Sat Jan 15 12:00:08 CET 2005

multiplets : see http://www.anorg.chem.uu.nl/people/staff/FrankdeGroot/ttmultiplets.htm

The other questions are rather simple :

You should never have more than one excitation in your cell.
The inelastic cross section for core loss is really very small, and not that many excitations occur.  Additionally, the small spatial extent of the core orbital 'localizes' the event, and there is no need to consider several simultaneous core loss excitations.  

If your two oxygen positions were inequivalent, they would have different initial/final states and therefore a different spectrum.  So you would have to do two separate calculations (one for each inequivalent oxygen), and then sum the spectra to get the 'total spectrum' of your material.  (That is not the same as exciting both atoms in one single calculation!)
However, in TiO2 there is only one oxygen equivalence class.  One calculation will do.
(Obviously, when you create a supercell, you will get more than one equivalence class.  But this is artificially introduced by yourself (in contrast to, eg., a 'real' impurity calculation), and all these classes represent the same atom from the simple unit cell.  Equivalently : it doesn't matter which of the images of the 'generating' atoms from the simple cell you choose to put the core hole on : all choices would give the same result, although some care may be required for orientation sensitive calculations.)

Kevin Jorissen

EMAT - Electron Microscopy for Materials Science   (http://webhost.ua.ac.be/emat/)
Dept. of Physics

UA - Universiteit Antwerpen
Groenenborgerlaan 171
B-2020 Antwerpen
Belgium

tel  +32 3 2653249
fax + 32 3 2653257
e-mail kevin.jorissen at ua.ac.be

________________________________

Van: wien-admin at zeus.theochem.tuwien.ac.at namens Shu Miao
Verzonden: za 15-1-2005 3:33
Aan: wien at zeus.theochem.tuwien.ac.at
Onderwerp: Re: [Wien] EELS of L3 Ti edge

Taking the case TiO2, both Ti and O will have  excitation. Should we
consider both when editing case.inc and case.in2? Or shoud we only modify
one atom each time and repeat the procedure twice to get Ti and O spectra,
respectively? If my unit cell contain 2 oxygen atoms, to get the O_K edge,
shoud I make one hole on each O?
Based on Peter's and Rebecca's replies, I make the following list to
calculate the EELS spectra,
**********
create supercell
remove electrons from case.inc and add them to case.in2
run scf cycles
reset electrons in case.in2 to the ground state number
run lapw2 -qtl
make case.innes
x initelnes
x tetra
x telnes
**********
Is this correct? Please comment.
For the multiplet programs memtioned by Jorissen, can they work well on
big unit cell containing 3 or more different elements?

Thanks

Shu  Miao

On Thu, 13 Jan 2005, Peter Blaha wrote:

> I'd just like to raise a few points you need to consider when you
> calculate spectra:
>
> TM oxides are often fairly correlated materials, so you might need LDA+U
> in some cases.
>
> EELS (and X-ray absorption) spectra have a core-hole as final state. In
> most cases this should NOT be neclected!
> You can simulate it with WIEN by creation of a small supercell and put
> a core hole on one of your atoms, promoting this electron into valence.
> /edit case.inc and reduce the core oppupation; edit case.in2 and add this
> electron.
> run_lapw
> edit case.in2 and set the number of electrons back to "normal"
> run you spectra.
>
> L2,L3: You may take the splitting from the core eigenvalues (case.scf) and
> overlay the spectra yourself (eg. in Excel) with the proper shift and
> with desired intensity ratio. I know this is not perfect, but not so bad
> either.
>
> Anyway, several people have shown that WIEN can be used quite successfully
> to calculate EELS spectra.
>
> Regards
>
> > I'm doing experimental and theoretical research on EELS of Ti (oxides mainly).
> > I found big differences in the experimental and computed spectra (for L3 edge)
> > - the computed spectra look very, very far from the experimental ones. We
> > tried to include other orbitals in the computation (changing the Ar core with
> > Ne and even He) but without any positive result. There are some articles in
> > which is shown that the expected ratio of the L3:L2 intensities should be 2:1
> > (on the basis of 2j+1 degerancy). It looks like that this can be the reason
> > for these differences with the experimental results. In the same articles is
> > shown that the ratio L3:L2 has to be 0.8 and in this case the spectral
> > features in the computed and experimental spectra are quite similar one to
> > each other. My question is it is possible to change somehow these ratios or
> > how we can improve the quality of the spectra? I would like just to notice,
> > that in the case of Cr we don't have such differences - the computed spectra
> > look quite good.
> >
> > Thanks in advance for your help
> > Best regards,
> > Emil Stoyanov
> >
> > _______________________________________________
> > Wien mailing list
> > Wien at zeus.theochem.tuwien.ac.at
> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> >
>
>
>                                       P.Blaha
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
> Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
> --------------------------------------------------------------------------
>
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