More specifically, is it true that calculating Raman spectra for metals is not
implemented in Quantum Espresso.
Hello,
the calculation of both dielectric matrix and Raman tensor in phonon is
only available for insulators and semiconductors, it also lacks gradient
correction and spin polarization. If you try to fool the code by not
using a smearing, you will get nonsensical dielectric tensor, as you
did. You can compute the frequency-dependent epsilon with the code
epsilon.x, this will allow you to compute the Raman response for a given
laser frequency.
You can compute the Raman tensor of metals using finite differentiation
of the frequency-dependent dielectric tensor along phonon displacement.
This can easily be done by hand:
1. take the displacements "v" of the phonon from the dynamical matrix
file (they are 3*n complex numbers, but at Gamma the imaginary parts are
zero)
2. move the atoms up and down this direction by a small amount (i.e.
±1.d-3 bohr)
3. compute the dielectric tensor in both cases (using epsilon.x)
4. compute the derivative. (epsilon(r+h v)-epsilon(r-h v))/2h
This will give you the Raman tensor in cartesian axes for the given phonon.
A more efficient alternative, is via the finite differentiation of
forces w.r.t an external electric field, as explained in
doi:10.1038/s41524-024-01236-3. The methodology should be available via
the Aiida interface.
kind regards
How does that work in VASP (for metals)?
No idea, you should its developers.
--
Dr. Lorenzo Paulatto
IR IMPMC - CNRS UMR 7590 / Sorbonne Université / MNHN
phone: +33 (0)1 442 79822 / telegram: lpaulatto
http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
23-24/423 B115, 4 place Jussieu 75252 Paris CX 05
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