Phase Transitions in a Model of Y-Shaped Molecules

Increasing attention in statistical mechanics is being given to non-spherical molecules, such as polypeptide chains and protein molecules. One example is provided by immunoglobulin, which has a ``Y'' shape. In this work, we determine the phase diagram of ``Y''-shaped molecules on a triangular lattice through Monte Carlo Grand Canonical ensemble simulation, using histogram reweighting and multicanonical sampling. We show that this system is a member of the Ising universality class through finite size scaling techniques. The molecules interact via the distal tips with the nearest neighbor distal ends of other molecules; There are no center to center interactions, center to tip, or molecule to lattice interactions included in this particular study. For low temperatures, multicanonical sampling was implemented to induce faster phase transitions in the simulation. Studying several system sizes, finite size scaling was used to determine the two phase coexistence curve, bulk critical temperature, and critical chemical potential.