  Metastable structures in macromolecular and colloidal systems are
non-equilibrium states that often have long lifetimes and cause difficulties in
simulating equilibrium. In order to escape from the long-lived metastable
states, we propose a newly devised method, molecular Monte-Carlo simulation of
systems connected to 3 reservoirs: chemical potential $\mu$, pressure $P$, and
temperature $T$. One of these reservoirs is adjusted for the thermodynamic
equilibrium condition according to Gibbs-Duhem equation, so that this adjusted
3rd reservoir does not thermodynamically affect phases and states. Additional
degrees of freedom, i.e. system volume $V$ and the number of particles $N$,
reduce kinetic barriers of non-equilibrium states and facilitate quick
equilibration. We show globally-anisotropic defect-free ordered structures,
e.g. string-like colloidal assembly, are obtained via our method.
