Advanced density functional approximations on 1T-TiSe₂ with charge density wave

Interplay between charge-density wave (CDW) and superconductivity in transition metal dichalcogenides has attracted intensive experimental and theoretical studies due to the application on energy-efficient devices. Particularly, the CDW instability in 1T-TiSe₂ is highly debated. The angle resolved photo emission spectroscopy finds the CDW transition and related insulating low-temperature phase with a gap of ~0.15 eV. While, the high-temperature phase could be either semimetallic or semiconducting given the very small indirect gap. So, the CDW in TiSe₂ might be purely driven by electronic instability, and 1T-TiSe₂ becomes a perfect candidate for digging into the role of exchange and correlation in CDW. Currently, the screened hybrid functional HSE06 is the best theoretical approximation to describe the electronic and phonon properties in the TiSe₂ CDW phase in comparison with experiments. Here, we employ the advanced density functional approximations meta-GGA to investigate the electronic and phonon properties of 1T-TiSe₂ with and without CDW. It is shown that the meta-GGA can improve the accuracy and efficiency of CDW simulations compared to standard exchange-correlation approximations and the screened hybrid functional HSE06, highlighting the importance of meta-GGAs for CDW related studies.