Calculation of the refractive indices of molecular crystals

The anisotropic optical properties of molecular crystals of general symmetry, which are characterized by three different refractive indices and corresponding optical axes, have been calculated by tensorial addition of the bond polarizabilities of all covalent bonds knowing the structure from X-ray diffraction analysis. As an example, refractive indices are given for β-phase fat crystals, viz glyceroltristearate and -tripalmitate, which are very hard to grow. Some of these refractive indices have been measured directly using the immersion method. Furthermore, average refractive indices of such crystals have been calculated by means of the Lorenz–Lorentz equation from the liquid data. As far as comparisons are possible, the theoretical values agree with experiments.