[Wien] EELS of L3 Ti edge

[Shu Miao]

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
> >
> > _______________________________________________
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> > Wien at zeus.theochem.tuwien.ac.at
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> >
>
>
>                                       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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