Understanding the structure of molecular liquids via combinations of molecular dynamics simulations and Reverse Monte Carlo modeling: Handling information deficiency

The problem of information deficiency, i.e., when the number of available diffraction (and/or EXAFS) experiments is (in many cases, much) lower than the number of partial radial distribution function in the system, is considered, with a focus on molecular liquids. Two approaches, both relying heavily on Reverse Monte Carlo (RMC) modeling [R.L. McGreevy, L. Pusztai, Molec. Simul. 1, 359 (1988)] are sketched: (1) molecular dynamics simulation, followed by RMC modeling ('RMCMD'), and (2) RMC modeling that incorporates the extensive use of interatomic potential functions ('RMC_POT'). We show that applying either method is useful, although the 'RMCMD' is restricted to smaller molecules. With larger molecules, the molecular structure begins to dominate the measurable total scattering structure factor and therefore, Reverse Monte Carlo is expected to play a more and more important role in conformational analyses in the liquid state.