THE PHASE-DIAGRAM OF A 2-DIMENSIONAL FLUID WITH INTERNAL QUANTUM STATES

A model molecular fluid with two-dimensional classical degrees of free dom and two internal quantum states is studied by path integral Monte Carlo simulations. The temperature-density phase diagram is obtained t o a high degree of precision using finite-size scaling techniques and local structure analysis methods. We locate the phase boundaries of ga s, liquid, square and hexagonal lattice solid phases together with a p referred internal quantum state resulting in tricritical and triple po ints. The simulation results for the liquid-solid transitions are comp ared with recent density functional theory calculations.