Patches

Some parts of elphmod (including examples) process the output of a modified version of Quantum ESPRESSO (QE). We provide the corresponding patches for different versions of QE. To apply them, go to the QE repository and run, e.g., the following commands:

git checkout qe-7.4
git apply /path/to/elphmod/patches/qe-7.4.patch
./configure
make pw pp ph epw

The patch files have been created using git diff -U1.

The following description applies to qe-6.7MaX-Release and higher versions. Since qe-7.4, the changes in EPW are part of QE and do not require a patch. The patch for qe-6.3-backports uses different formats for input and output, which requires using elphmod.elph.Model(old_ws=True).

Changes in PHonon

The following inputs are used for constrained density-functional perturbation theory (cDFPT) [Nomura and Arita, Phys. Rev. B 92, 245108 (2015)]. If not set, a standard DFPT calculation is done.

  • cdfpt_bnd: Definition of cDFPT active subspace via list of band indices. The band indices are defined by QE, where bands are sorted by energy.

  • cdfpt_orb: Definition of cDFPT active subspace via list of orbital indices. This requires that a projwfc.x calculation for the complete uniform k mesh used in the phonon calculation is done before. The orbital indices are defined in the output file of projwfc.x. If n orbitals are specified, for each k point, the n states with the largest projection onto the subspace spanned by these n orbitals are selected. If cdfpt_bnd is also specified, up to n states among these bands are chosen.

  • bare: Suppress electronic response to atomic displacements? This corresponds to a cDFPT active subspace containing all states.

Additionally, the option electron_phonon = 'defpot' prints the electron-phonon matrix elements in Ry/bohr in the Cartesian basis to standard output.

Changes in EPW

If epwwrite is enabled, the file wigner.fmt is written. It contains the Wigner-Seitz vectors and degeneracies corresponding to the electron-phonon matrix elements in the localized representation in outfir/prefix.epmatwp.