The Impact of Electron-Phonon Interactions in Monolayer Materials from First-Principles

We utilize first-principles theory to investigate the optoelectronic properties of a series of monolayer materials, emphasizing the role of electron-phonon interactions, a phenomenon that can dominate the properties of low dimensional systems due to their reduced screening. We utilize first-principles density functional theory (DFT) and many-body perturbation theory (MBPT) to describe excited state transitions and the special displacement (SD) method recently developed by Zacharias and Giustino to describe the role of phonons. For monolayer GeSe, a promising monochalcogenide material, our calculations predict that the optical absorption spectrum is red-shifted by ~ 0.1 eV and that the Wannier exciton wavefunction is distorted due to electron-phonon interactions, with optical phonons at ~100 cm^-1 coupling most strongly to the excitonic state. To better understand the role of exciton-phonon interactions in low dimensions, we study the band gap renormalization for a series of 2D materials. For ~100 monolayer materials, we compute the gap with and without the presence of phonons within DFT and the SD approach. The connection between different physical descriptors with band gap renormalization are explored and highlighted using a data-driven approach, demonstrating that the strength of electron-phonon interactions is highly dependent on the bonding structure. Overall, this framework allows for a systematic theoretical exploration of the influence of phonons on optical properties.