Validation of calculations based on electron-phonon matrix elements in Abinit and QE/Yambo (original) (raw)

Abstract

First-principles electronic-structure codes are in constant development and evolution to adapt with increasing computational capabilities and simulation sizes. Hence, verification and validation of codes, as well as new theoretical methods, are of utmost importance if one wants to provide reliable results. In this work we present a rigorous and careful study of all the quantities that enters into the calculation of the zero point motion renormalization of the direct band gap of diamond due to electron-phonon coupling. This study has been done within the Allen-Heine-Cardona (AHC) formalism [1] as implemented into Abinit [2] and Yambo [3] on top of Quantum Espresso [4]. In this work we aim at quantifying the agreement between the codes for the different quantities of interest. This study shows that one can get less than 10−7Ha/at10^{-7}Ha/at10−7Ha/at differences on the total energy, 0.01 cm$^{-1}$ on the phonon frequencies, 0.005 on the electron-phonon matrix elements and less than 1 meV on the zero-point-motion renormalization. At the LDA level, the converged direct band gap renormalization in diamond due to electron-phonon coupling in the AHC formalism is -408 meV (reduction of the band gap). [1] P. B. Allen and M. Cardona, Phys. Rev. B 24, 7479 (1981). [2] X. Gonze et al, Computer Physics Communications 180, 2582 (2009). [3] E. Cannuccia and A. Marini, Phys. Rev. Lett. 107, 255501 (2011). [4] P. Giannozzi et al., Journal of Physics: Condensed Matter 21, 395502 (2009).

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