  In recent years the statistical mechanics of non-spherical molecules, such as
polypeptide chains and protein molecules, has garnered considerable attention
as their phase behavior has important scientific and health implications. 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 hexagonal lattice
through Monte Carlo Grand Canonical ensemble simulation, using histogram
reweighting, multicanonical sampling, and finite-size scaling. We show that (as
expected) this model is a member of the Ising universality class. For low
temperatures, we implemented multicanonical sampling to induce faster phase
transitions in the simulation. By studying several system sizes, we use
finite-size scaling to determine the two phase coexistence curve, including the
bulk critical temperature, critical chemical potential, and critical density.
