Fig. 2. (a) Polarizability anisotropy and HOMO–LUMO gaps of the [BS3], [HgCl2], [HgBr2], [HgI2], [HgS2], and [HgSe2] units; (b) experimental Raman spectrum of HgBr2; (c) UV-vis-IR transmittance spectrum collected from the single crystal (inside: the photograph of single crystal HgBr2 plate); (d) crystallographic orientation and birefringence measurement of the HgBr2 crystal; (e) the calculated birefringence values of HgBr2.
