Molecular liquids are a huge class of disordered systems, possessing utmost importance (cf. water and aqueous solutions — with a little exaggeration, our body is a mixture of aqueous solutions!). They are therefore natural targets of structural studies in general, and of Reverse Monte Carlo structural modeling in particular. Diffraction data on their own cannot tell if the measured sample consists of molecules: the concept of the molecule as an object with fixed topology has to be added as a constraint. Several ways for this process will be mentioned, including the so-called ‘fixed neighbours constraints’: various successful applications, including carbon-tetrachloride, pure water and aqueous electrolyte solutions, as well as pure lower alcohols, will be presented.
However, for more complicated (than, say, 1-propanol) molecules, this simple neighbor-list based concept is no longer feasible: a more general way of dealing with molecules may be borrowed from constrained molecular dynamics (MD) simulations. During the process of building elements of MD into Reverse Monte Carlo modeling, it has been found that running MD in parallel with RMC is rather fruitful idea; the case of electrolyte solutions will be shown as examples for this ‘tandem’.
Wigner Research Centre for Physics, Hungarian Academy of Sciences, Budapest, Hungary