Electronic structure of TiSe$_2$ from a quasi-self-consistent G$_0$W$_0$ approach

TL;DR

This paper introduces a quasi-self-consistent G0W0 approach based on RPA and hybrid DFT to accurately describe the electronic structure of TiSe2, capturing its phase transitions and properties more reliably than traditional methods.

Contribution

The work develops a new quasi-self-consistent G0W0 method that improves the starting point for electronic structure calculations of TiSe2 and similar materials.

Findings

High-temperature TiSe2 is a semi-metal with experimental band structure agreement.

The hybrid functional accurately reproduces the low-temperature charge density wave phase.

Self-consistency is crucial for correctly describing TiSe2 and TiS2.

Abstract

In a previous work it was shown that the inclusion of exact exchange is essential for a first principles description of both the electronic- and the vibrational properties of TiSe$_2$, M. Hellgren et al. [Phys. Rev. Lett. 119, 176401 (2017)]. The $GW$ approximation provides a parameter-free description of screened exchange but is usually employed perturbatively ($G_0W_0$) making results more or less dependent on the starting point. In this work, we develop a quasi-self-consistent extension of $G_0W_0$ based on the random phase approximation (RPA) and the optimized effective potential of hybrid density functional theory. This approach generates an optimal $G_0W_0$ starting-point and a hybrid exchange parameter consistent with the RPA. While self-consistency plays a minor role for systems such as Ar, BN and ScN, it is shown to be crucial for TiS$_2$ and TiSe$_2$. We find the high-temperature phase of TiSe$_2$ to be a semi-metal with a band structure in good agreement with experiment. Furthermore, the optimized hybrid functional agrees well with our previous estimate and therefore accurately reproduces the low-temperature charge density wave phase.