INTERACTION FORCES IN CHARGED COLLOIDS - INVERSION OF STATIC STRUCTURE FACTORS

A simple, easily usable ''predictor-corrector'' inversion method is pr esented for extracting the effective pair potential u(r) from static s tructure factor S(q) of colloidal dispersions and liquids. The method, based on the Ornstein-Zernike integral equation, replaces the unknown bridge function B(r) in the closure with an iteratively obtained hard -sphere bridge function B-d(r). The accuracy of the method is examined by direct determination of B(r) using simulations for extreme example s of pair potential appropriate for charged dispersions. An example of the application of the method to liquid metals is also presented. The results demonstrate the need for using S(q) over the full range of q' s [especially S(q)'s for sufficiently low values of q] for obtaining t he crucial details of u(r). They further show the fallacies associated with the previous analyses of S(q) that have fueled the controversy c oncerning the nature of interaction forces in charged colloids and sug gest the types of data needed for extracting u(r) for colloidal, Coulo mbic, and simple fluids.