Electronic structure of TiSe2 from a quasi-self-consistent G(0)W(0) 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.