[gpaw-users] Polarizability Tensor

[Thomas Olsen]

Hi Frank

Th get_polarizability method actually only gives the longitudinal part of the polarizability - the component parallel to q. The direction keyword will essentially be ignored if you supply a finite q and is only relevant for the limiting case of q->0. I think however, that you could get the full polarizability tensor quite easily in this limit. But it may require a few hacks...

/Thomas
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Fra: gpaw-users-bounces at listserv.fysik.dtu.dk [gpaw-users-bounces at listserv.fysik.dtu.dk] på vegne af Frank von Horsten via gpaw-users [gpaw-users at listserv.fysik.dtu.dk]
Sendt: 14. juni 2016 12:15
Til: gpaw-users at listserv.fysik.dtu.dk
Emne: [gpaw-users] Polarizability Tensor

Dear all,

I would like to calculate Raman scattering activities with GPAW. For that I need the polarizability tensor.

I saw that there is a get_polarizability() function in the DielectricFunction class. However, I am relatively new to GPAW and just about to familiarize myself with the program. Hence, I'm not sure how to use it correctly.

Can anyone give me some insight how to calculate the elements of the polarizability tensor?

To be more specific, let's say we start with an ASE atoms object "atoms" and have defined a GPAW calculator "calc":
0.) atoms.set_calculator(calc)
1.) atoms.get_potential_energy()
2.) calc.diagonalize_full_hamiltonian(nbands=X)
3.) calc.write("system.gpw",all)
4.) df=DielectricFunction('system.gpw',hilbert=not True, eta=0.1, ecut=10, frequencies=omega)
5.) a0,a=df.get_polarizability(filename=None,direction='x')

Would that be the way to calculate the matrix element \alpha_xx at frequency omega?
If so, I would understand that by changing the direction='y' or 'z' I would get \alpha_yy and \alpha_zz. However, I don't know how to obtain the off diagonal elements xy etc.
So I reckon that there is something fundamental, which I misunderstood so far.

Any hints would be greatly appreciated! I also saw that there is a new ResonantRaman class within ASE. Does anyone know if the is already usable or still work in progress?

Thanks and best wishes,

Frank
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