[Wien] Raman cross section

[Peter Blaha]

I'm NOT an expert in Raman spectra calculations, but from literature I know
the work of C.Ambrosch-Draxl et al. (several papers, but see eg.
J. Spitaler, E. Ya. Sherman, and C. Ambrosch-Draxl,Phys. Rev. B 75 (2007) 014302

As far as I understood, the Raman intensities for EACH phonon and EACH polarization
(and even for particular exitation energies) are obtained by looking at the
changes of the dielectric function with a particular phonon mode.


I don't know if a static electric field can also be used for that purpose (at least
for Berry charges I would have guessed so). Maybe the "brute force" methods suffer
from numerical problems ?
How large a non-linear effect (or slope) would you expect ???

PS: There is a new development underway, but since I'm not really involved, I cannot say
more.


Am 08.08.2011 11:38, schrieb Torsten Weissbach:
> Hello,
>
> for some time I have tried to calculate the Raman tensor for GaAs using
> the second derviative of the force with respect to the electrical field
> with WIEN. The field was applied as sawtooth potential (the default
> choice) over two supercells with c parallel to the 100 and 110 fcc
> directions. The symmetry was lowered  by removing all symmetry
> operations from the .struct and adding all L,M values for the lattice
> harmonics in .in2. However, it seems impossible to produce any
> non-linear behaviour of the forces, which should occur at least in case
> of the 110 field. Additionally, the Born effective charge, which can be
> calculated from the slope, is also not in accordance with the known
> value. Now I'm puzzled whether there are still other options which
> should be altered or I made mistakes, and if it is principally possible
> to use the efield in lapw0 for this purpose.
> Thanks for your help,
> Torsten
>
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                                       P.Blaha
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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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