# Critical role of the exchange interaction for the electronic structure and charge-density-wave formation in TiSe2

## TL;DR

This paper demonstrates that including screened exchange via hybrid functionals in density functional theory provides a comprehensive understanding of TiSe2's electronic structure and charge-density-wave formation, aligning well with experimental observations.

## Contribution

The study shows that hybrid functionals accurately capture electron-electron interactions, stabilizing the CDW phase and matching experimental electronic and vibrational properties of TiSe2.

## Key findings

- Hybrid functionals distinguish Ti-d and Se-p states effectively.
- Enhanced electron-phonon coupling drives the CDW transition.
- Generated CDW phase matches experimental band structure and phonon data.

## Abstract

We show that the inclusion of screened exchange via hybrid functionals provides a unified description of the electronic and vibrational properties of TiSe2. In contrast to local approximations in density functional theory, the explicit inclusion of exact, non-local exchange captures the effects of the electron-electron interaction needed to both separate the Ti-d states from the Se-p states and stabilize the charge-density-wave (CDW) (or low-T) phase through the formation of a p-d hybridized state. We further show that this leads to an enhanced electron-phonon coupling that can drive the transition even if a small gap opens in the high-T phase. Finally, we demonstrate that the hybrid functionals can generate a CDW phase where the electronic bands, the geometry, and the phonon frequencies are in agreement with experiments.