Applications of computational geometry to the molecular simulation of interfaces

The identification of the interfacial molecules in fluid-fluid equilibrium is a long-standing problem in the area of simulation. We here propose an alternative point of view, making use of concepts taken from the field of computational geometry, where the definition of the "shape" of a set of points is a well-known problem. In particular, we employ the alpha -shape construction which, applied to the positions of the molecules, selects a shape and identifies its boundary points, which we will take to define our interfacial molecules. A single parameter needs to be fixed (the "alpha" of the alpha shape), and several proposals are examined, all leading to very similar choices. Results of this methodology are evaluated against previous proposals, and seen to be reasonable.