  The electronic and optical properties of 2D hexagonal boron nitride are
studied using first principle calculations. GW and BSE methods are employed in
order to predict with better accuracy the excited and excitonic properties of
this material. We determine the values of the band gap, optical gap, excitonic
binding energies and analyse the excitonic wave functions. We also calculate
the exciton energies following an equation of motion formalism and the Elliot
formula, and find a very good agreement with the GW+BSE method. The optical
properties are studied for both the TM and TE modes, showing that 2D hBN is a
good candidate to polaritonics in the UV range. In particular it is shown that
a single layer of h-BN can act as an almost perfect mirror for ultraviolet
electromagnetic radiation.
