Phonons are collective atomic vibrations in crystals that govern many physical phenomena ranging from electrical and thermal transport to superconductivity and light absorption. When calculating phonon properties, it is important to consider that the interactions between two particles in a crystal are not bare but screened by other particles. The effect of this screening on the atomic vibrations is encoded in their self-energy. However, computing the exact phonon self-energy presents a formidable challenge requiring approximations to describe realistic materials accurately. The most common approximation has been repeatedly criticized for double counting screening effects. We provide the essential benchmarks to settle this long-standing debate.
Through calculations for realistic materials and models, we show that the common approximation can describe changes in the phonon self-energy more accurately than alternatives retaining the mathematical structure of the exact self-energy. We achieve this by separating the problem into a low- and a high-energy part to bridge the gap between the bare and the screened interactions.
This separation opens the thrilling possibility of tackling the dynamics of the electron-phonon coupling and phonons in materials where the concept of independent particles breaks down.
https://journals.aps.org/prx/abstract/10.1103/PhysRevX.13.041009
Authors: Jan Berges, Nina Girotto, Tim Wehling, Nicola Marzari and Samuel Poncé