  We applied a multicanonical algorithm (entropic sampling) to a
two-dimensional and a three-dimensional Lennard-Jones system with
quasicrystalline and glassy ground states. Focusing on the ability of the
algorithm to locate low lying energy states, we compared the results of the
multicanonical simulations with standard Monte Carlo simulated annealing and
molecular dynamics methods. We find slight benefits to using entropic sampling
in small systems (less than 80 particles), which disappear with larger systems.
This is disappointing as the multicanonical methods are designed to surmount
energy barriers to relaxation. We analyze this failure theoretically, and show
(1) the multicanonical method is reduced in the thermodynamic limit (large
systems) to an effective Monte Carlo simulated annealing with a random
temperature vs. time, and (2) the multicanonical method gets trapped by
unphysical entropy barriers in the same metastable states whose energy barriers
trap the traditional quenches. The performance of Monte Carlo and molecular
dynamics quenches were remarkably similar.
