First-principles calculations of phonons are often based on the adiabatic approximation, and Brillouin-zone samplings that might not always be sufficient to capture the subtleties of Kohn anomalies. These shortcomings can be addressed through corrections to the phonon self-energy arising from the low-energy electrons. A well-founded correction method exists [1], which only relies on adiabatically screened quantities. However, many-body theory suggests to use one bare electron-phonon vertex in the phonon self-energy [2] to avoid double counting [3]. In our recent work [4], we assess the accuracy of both approaches in estimating low-temperature adiabatic phonon dispersions, and we offer a third strategy based on downfolding to partially screened phonons and interactions [5]. Generalizations of these schemes beyond the harmonic approximation are possible and provide access to the anharmonic potential-energy landscape of charge-density-wave materials [6]. We also comment on their applicability to the nonadiabatic case [3, 7, 8].

 

[1] M. Calandra, G. Profeta, and F. Mauri, Phys. Rev. B 82, 165111 (2010)

[2] F. Giustino, Rev. Mod. Phys. 89, 015003 (2017)

[3] A. Marini, Phys. Rev. B 107, 024305 (2023)

[4] J. Berges, N. Girotto, T. Wehling, N. Marzari, and S. Poncé, arXiv:2212.11806 (2022)

[5] Y. Nomura and R. Arita, Phys. Rev. B 92, 245108 (2015)

[6] A. Schobert, J. Berges, E. G. C. P. van Loon, M. A. Sentef, S. Brener, M. Rossi, and T. O. Wehling, arXiv:2303.07261 (2023)

[7] G. Stefanucci, R. van Leeuwen, and E. Perfetto, arXiv:2303.02102 (2023)

[8] A. Marini, arXiv:2303.09869 (2023)