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

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 TiSe2, 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 TiS2 and TiSe2. We find the high-temperature phase of TiSe2 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.

Automated summary

The study demonstrates the importance of including exact exchange for describing the electronic and vibrational properties of TiSe2. The developed quasi-self-consistent extension of G(0)W(0) based on the random phase approximation and hybrid density functional theory is crucial for systems like TiS2 and TiSe2, providing an optimal starting point and consistent hybrid exchange parameters. The high-temperature phase of TiSe2 is found to be a semimetal with a band structure in good agreement with experimental results, while the optimized hybrid functional accurately reproduces the low-temperature charge-density-wave phase.