Semiempirical Calculations of Ionic Polarizabilities and van der Waals Potential Coefficients for the Alkaline-Earth Chalcogenides

Electronic polarizabilities for the ions of the alkaline-earth chalcogenides have been calculated by assuming an additivity law within the family of salts and a Lorentz factor of $\frac{4}{3}\pi$, and using experimental refractive indices and interionic distances. It is shown that the additivity assumption is well obeyed, and the Lorentz factor value of $\frac{4}{3}\pi$ gives the best fit to the data. Each polarizability obtained has been related to a mean excitation or characteristic energy for the ion, and hence the coefficients of the dipole-dipole and dipole-quadrupole terms of the van der Waals interaction energy derived.