Effect of the range of the potential on two-dimensional melting

Abstract

Insights into the melting of two-dimensional simple atomic systems are presented from investigation of the effect of the range of the interatomic potentials on the existence of hexatic phase, using molecular-dynamics simulations under isobaric-isothermal as well as isochoric-isothermal conditions. We find that longer-ranged interatomic potentials are important for the formation of stable hexatic phases. A schematic plot of the phase diagrams with a hexatic regime is presented capturing the overall shape of the phase boundaries and the behavior of the system. As the range of the potential is varied, the pressure-temperature phase diagram exhibits distinct topologies. For soft longer-ranged Morse potentials, the hexatic phase can coexist with the gaseous phase. On the other hand, as the range gets shorter, the onset point of the hexatic phase, i.e., the lower bound pressure of the hexatic region in the phase diagram, gets shifted upward, and the hexatic phase region no longer touches the gaseous phase.