Organic ices: methanol monohydrate

Methanol monohydrate is one of several crystalline phases present in the methanol-water system. At ambient conditions of pressure, methanol monohydrate has a polar disordered structure. Here we study its behavior under pressure using the density-functional theory in the ABINIT implementation. We propose several initial ideally ordered configurations that we optimize as a function of pressure. We characterize the compressibility and the relative stability of these different configurations under pressure. Two ideally ordered monoclinic structures with symmetry Cc and P21 are proposed as the most energetically favorable ones. Temperature-induced hydrogen disordering and reordering can easily turn them one into the other. We characterize a series of physical properties and their variation under pressure. We find a considerably large spontaneous polarization to occur which produces surface dipoles able to induce preferred overgrowth of other ices or clustering of other more complex polar organic molecules.