Electronic structure of TiSe2 from a quasi-self-consistent G0W0 approach

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 $\mathrm{Ti}{\mathrm{Se}}_{2}$, 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 (${G}_{0}{W}_{0}$), making results more or less dependent on the starting point. In this work, we develop a quasi-self-consistent extension of ${G}_{0}{W}_{0}$ based on the random phase approximation (RPA) and the optimized effective potential of hybrid density functional theory. This approach generates an optimal ${G}_{0}{W}_{0}$ 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 $\mathrm{Ti}{\mathrm{S}}_{2}$ and $\mathrm{Ti}{\mathrm{Se}}_{2}$. We find the high-temperature phase of $\mathrm{Ti}{\mathrm{Se}}_{2}$ to be a semimetal 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.