Phase transitions in a mercury monolayer

The physical properties of low-dimensional systems are sometimes vastly different from the properties of their bulk counterparts. Recently, Miedema and Dorleijn made the very interesting prediction, based on semiempirical theory, that there might exist a wide range of substrates on which a monolayer of Hg will be nonmetallic. In a fully ab initio study, we have calculated the total energy of free monolayers of Hg as a function of the lattice constant using local-density theory and the full-potential linearized augmented-plane-wave method. There are at least three different phases which are found to play an important role. Near the energy minimum, the variation of the total energy is small over a wide range of values of the lattice parameter, which includes regions of metallic and insulating behavior. Hence our results predict that the interaction with the substrate will determine whether a Hg monolayer is metallic or not.