Understanding disordered structures: Reverse Monte Carlo analyses of diffraction data on liquids and amorphous materials

Dr. László Pusztai, Wigner Research Centre for Physics, Hungarian Academy of Sciences Reverse Monte Carlo modeling is a (by now) common tool for studying structural disorder in liquids, and amorphous and crystalline materials alike. RMC needs high quality experimental data, as input information, from neutron- and/or X-ray diffraction (including anomalous X-ray scattering), and/or EXAFS measurements – and, as a matter of fact, from any other kind of experiments where the measured signal is calculable from particle coordinates. The primary results of Reverse Monte Carlo calculations are large sets of particle coordinates (“configurations”) that are consistent with each set of input experimental data. These configurations may be used for subsequent analyses of the atomic structure. Here I will briefly introduce the basics of the RMC method and then switch to showing examples, from molecular liquids like tin-tetraiodide (SnI4), via aqueous solutions of electrolytes (e.g., CsCl, CsBr, CsI in water), to covalent glasses (containing Ge, Se, Sb, Te). These materials all contain elements in which X-ray absorption edges suitable for EXAFS spectroscopy exist. The possibility of using diffraction and EXAFS experiments, molecular dynamics simulations and Reverse Monte Carlo modeling will be examined for the liquid materials mentioned above.