First-principles investigation of the charge-density-wave instability in 1T-TaSe2

The charge-density-wave (CDW) instability in 1T-TaSe2 is investigated as a function of pressure. Density-functional calculations accurately capture the instability at ambient pressures and predict the suppression of the CDW distortion under pressure. The instability is shown to be driven by softening of selected phonon modes due to enhanced electron-phonon matrix elements, rather than by nesting of the Fermi surface or other electronic mechanisms. In addition, the electronic structure of 1T-TaSe2 and 1T-TaS2 are compared to investigate why the electronic transition that accompanies the structural transition in the sulfide is not observed in the selenide. Finally, the possibility of electron-phonon superconductivity in compressed TaSe2 is discussed.