Influence of exchange-correlation functionals on dielectric properties of rutile TiO2

We investigate dielectric properties of rutile TiO2 using various exchange-correlation energy functionals such as local-density approximation (LDA), LDA + U method, and hybrid functionals. It is found that the computed dielectric constants significantly depend on the functional type, which originates from hardening or softening of phonon modes. While LDA provides the best result among the tested functionals, hybrid functionals and LDA + U methods significantly overestimate and underestimate dielectric constants, respectively. The underestimation by LDA + U is most alarming as it is not alleviated by adjusting lattice parameters, which implies that interatomic interactions are fundamentally affected by LDA + U. Furthermore, the LDA + U method also underestimates the dielectric constant of cubic SrTiO3. The present results suggest that special cares are needed in applying the LDA + U method to a system including TiO2 and SrTiO3.

► Test of various energy functionals against dielectric constants of TiO2.
► Overestimation by hybrid functionals can be resolved by adjusting lattice parameters.
► Significant underestimation by LDA + U methods is indicative of incorrect lattice dynamics.