[gpaw-users] Electron-phonon interaction calculations

[Anastasiia Vladimirova]

Dear GPAW community,

I am trying to calculate total phonon scattering rate, using the GPAW software and my results are approximately 1000 times higher than what is reported in literature,

I am using this tutorial: https://wiki.fysik.dtu.dk/gpaw/tutorialsexercises/vibrational/elph/elph.html, but in the final program, gmatrix.py, I use different code because I need the sqrt prefactor and all BZ for phonons:

from gpaw import GPAW
from gpaw.elph import ElectronPhononMatrix
import numpy as np

calc = GPAW("scf.gpw")
atoms = calc.atoms
elph = ElectronPhononMatrix(atoms, 'supercell', 'elph')

g_sqklnn = elph.bloch_matrix(calc,
                             savetofile=True, prefactor=True)

I assume that mistake comes from the sqrt prefactor, that is why I my questions are:

1) Did anyone had similar problem?

2) What should be m in the sqrt prefactor? I the code it says it is effective mass, which I assume is dimensionless.
In the tutorial it says that it is the sum of the masses of all the atoms in the unit cell.
 In the first case the finall dimensions for sqrt(...) *<||> will be units of energy, which is correct.
In the second case the units will be energy/length, which is wrong.
In accordance to the code itself it uses mass of the nuclei devided by the electron mass:

        # Multiply prefactor sqrt(hbar / 2 * M * omega) in units of Bohr
        if prefactor:
            # potential BUG: M needs to be unit cell mass according to
            # some sources
            amu = units._amu  # atomic mass unit
            me = units._me  # electron mass
            g_lnn /= np.sqrt(2 * amu / me / units.Hartree *
                             omega_ql[0, :, np.newaxis, np.newaxis])
            # Convert to eV
            return g_lnn * units.Hartree  # eV
        else:
            return g_lnn * units.Hartree / units.Bohr  # eV / Ang

Kind regards,
Anastasiia



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