Study of the near-edge optical properties of monoclinic HfO$_2$ from first-principles*

HfO$_2$ is a wide band gap dielectric material, that has applications in optical coatings, rendering the importance of a precise description of its optical properties. The full understanding, however, has been limited by the lack of a consistent explanation of a shoulder-like feature near the absorption onset, reported in multiple experimental studies. In this work, by solving the Bethe-Salpeter equation (BSE) for the optical polarization function, we compute the optical spectra of monoclinic HfO$_2$ from first-principles. From these results we show that the shoulder-like effect is intrinsic to the crystal and is related to excitonic effects. Further, we show that since HfO$_2$ is a polar material, lattice screening, especially beyond the current static screening approximation, can potentially be important in describing dielectric screening of the electron-hole Coulomb interaction. In this work, we explored the effect of \emph{dynamical} lattice screening in HfO$_2$, and aim at describing the influence of lattice screening on the near-edge optical spectra.