EPW is the short name for “Electron-phonon Wannier”. EPW is an open-source F90/MPI code which calculates properties related to the electron-phonon interaction using Density-Functional Perturbation Theory and Maximally Localized Wannier Functions. The development of EPW is led by Hyungjun Lee, Samuel Poncé, Roxana Margine, and Feliciano Giustino.

The most recent reference technical manuscript is:

EPW is distributed as part of the Quantum ESPRESSO suite.

The code was written by Feliciano Giustino (EPW v1) and Jesse Noffsinger (EPW v2) while in the Cohe/Louie Group at the University of California, Berkeley. Brad Malone (Harvard) and Cheol-Hwan Park (Seoul National University) contributed with tests and benchmarks. Roxana Margine implemented the anisotropic Eliashberg theory while in the Giustino group at the University of Oxford (EPW v3). Carla Verdi developed the electron-phonon interpolation for polar materials including Froehlich correction while in the Giustino group at Oxford. Samuel Poncé made the code compatible with Quantum Espresso v5, optimized it, and developed an automatic test-farm for the code (EPW v4). He also implemented the electronic transport module while in the Giustino group at the University of Oxford (EPW v5). Hyungjun Lee introduced support for PAW pseudopotentials, multi-level parallelism, and HDF5 while in the Giustino group at the University of Texas at Austin (EPW v6, to be released).

EPW is based on the method introduced in F. Giustino et al, Phys. Rev. B 76, 165108 (2007). An extended description of the first public release has been published in J. Noffsinger et al, Comput. Phys. Comm. 181, 2140 (2010). The extension of EPW to include the anisotropic Midgal-Eliashberg theory is based on the method described in E. R. Margine et al, Phys. Rev. B 87, 024505 (2013).

The EPW Collaboration includes: Hyungjun Lee, Chao Lian, Joshua Leveillee, Weng Hong Sio, Feliciano Giustino (UT Austin), Samuel Poncé (EPFL), Hari Paudyal, Roxana E. Margine (SUNY Binghamton), Francesco Macheda, Nicola Bonini (Kings College London), Xiao Zhang, Emmanouil Kioupakis (U Michigan Ann Arbor).

EPW is developed under git within the GitLab portal.

As of May 2020, EPW consists of 48,902 Fortran lines (including comments).

## Computing electron-phonon properties with EPW¶

EPW can be used to compute:

• The total electron-phonon coupling strenght $$\lambda$$

• The anisotropic Eliashberg spectral function $$\alpha^2F$$

• The transport spectral function $$\alpha^2 F_{\rm tr}$$

• The anisotropic superconducting gap $$\Delta_{n{\bf k}}$$ within the Eliashberg theory

• The electron and phonon self-energies arising from electron-phonon interaction

• The phonon linewidths and lifetimes arising from electron-phonon interaction

• The electron linewidths and lifetimes arising from electron-phonon interaction

• The temperature-dependence of the carrier lifetimes

• The spectral functions needed for the calculation of ARPES spectra

• The temperature-dependent electron and hole mobility $$\mu$$ within the Boltzmann transport formalism

## Introducing EPW¶

Presentation of EPW during the Quantum Espresso Developers meeting in Trieste, Italy, January 2017

Presentation of EPW during the Quantum Espresso Linear Response workshop in Trieste, Italy, January 2016