Electron correlations rule phonon-driven instability in single layer TiSe$_2$

Abstract

We investigate the controversial case of charge-density-wave (CDW) order in single layer 1T-TiSe2 by employing the density functional perturbation theory with on-site Hubbard interactions. The results emphasize the crucial role of electron correlations via Hubbard corrections in order to capture the accurate electronic structure, low-and high-temperature limits of the CDW phonon mode, and temperature-charge phase diagram, all overestimated with semi-local functionals. According to our analysis, the CDW order in TiSe2 is mainly governed by momentum dependent electronphonon coupling and electron correlations, while other mechanisms, such as exchange and excitonic interactions, might only support its formation.