EXAFS as a probe of atom-atom interaction potentials: AgI and CuI

The extended fine structure on the X-ray absorption cross section (EXAFS) depends sensitively upon the details of the nearest-neighbour peak in the atom-atom pair correlation function. It follows that EXAFS data can be helpful in determining the short-range portion of atom-atom pair interaction potentials such as are the starting point for molecular dynamics (MD) calculations. The cation-anion pair correlation functions g(r) obtained from MD calculations on superionic AgI and CuI are compared with EXAFS data. The nearest-neighbour peak in the MD g(r) begins at too short a cation-anion separation and is too broad to be consistent with the data. The causes and ramifications of this are discussed.