Understanding complexity of hydrogen-bonded liquids through Voronoi entropy

In this paper we study the short order of liquids using Voronoi entropy (SVor), computed using Voronoi Polyhedra (VP) tessellations. Voronoi tessellations partition a plane with n seeds into polyhedrons, in which each polyhedron has exactly one seed and every location within a given polyhedron is nearest to its generating seed, rather than to any other seed. The distribution of these VP is used to determine the Voronoi entropy (SVor), which shares similarities with the Shannon measure of information (H). Such studies, however, have been largely restricted to two-dimensional analysis. In this study SVor is used to quantify the orderliness of the three-dimensional structures of hydrogen-bonded systems (water, methanol, ethanol, and 1-propanol), as well as binary mixtures (methanol-ethanol, methanol-1-propanol, and ethanol-1-propanol) through molecular dynamics simulations. SVor is calculated for the VP considering all atom types and oxygen atoms to exclusively study the hydrogen bonds. The SVor for all atoms shows that the smaller molecules have a more ordered structure than the larger ones whereas the SVor calculated considering only oxygen atoms decreases as the alkyl chain length of the molecules increases indicating the smaller molecules have more ways to form hydrogen bonds than the larger ones. SVor calculated for binary mixtures for varying concentrations shows a similar trend.