Ea. Jagla, PHASE-BEHAVIOR OF A SYSTEM OF PARTICLES WITH CORE COLLAPSE, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 58(2), 1998, pp. 1478-1486
The pressure-temperature phase diagram of a one-component system, with
particles interacting through a spherically symmetric pair potential
in two dimensions, is studied. The interaction consists of a hard core
plus an additional repulsion at low energies. It is shown that at zer
o temperature, instead of the expected isostructural transition due to
core collapse occurring when increasing pressure, the system passes t
hrough a series of ground states that are not triangular lattices. In
particular, depending on parameters, structures with squares, chains,
hexagons, and even quasicrystalline ground states are found. At finite
temperatures the solid-fluid coexistence line presents a zone with ne
gative slope (which implies melting with decreasing in volume) and the
fluid phase has a temperature of maximum density, similar to that in
water.