RELATIONSHIP BETWEEN BOND CHARGE AND THE SZIGETI EFFECTIVE CHARGE IN ALKALI-HALIDES

The effective bond charge q(eff), as related to experimental values of the third-order nonlinear optical susceptibility, is determined for some alkali halides within the bond polarizability interpretation of the Phillips-Van Vechten theory. It is shown that the charge decreases strongly for the more ionic alkali halides. Also, monotonic dependencies of q(eff) on other parameters which correlate with the crystal ionicity, like the Szigeti effective charge and the Sanderson partial charge, are found. The results obtained suggest that for alkali halides with the same cation, q(eff) is a linear function of the Phillips-Van Vechten ionicity.