Equilibrium macroscopic structure revisited from spatial constraint

In classical systems, we reexamine how macroscopic structures in equilibrium state connect with spatial con- straint on the systems: e.g., volume and density as the constraint for liquids in rigid box, and crystal lattice as the constraint for crystalline solids. We reveal that in disordered states, equilibrium macroscopic structure, depend- ing on temperature and on multibody interactions in the system, is characterized by a single special microscopic structure independent of temperature and of interactions. The special microscopic structure depends only on the spatial constraint. We demonstrate the present findings providing (i) significantly efficient and systematic prediction of macroscopic structures for possible combination of constituents in multicomponent systems, and (ii) unique and accurate determination of multibody interactions in given system from measured macroscopic structure, without performing trial-and-error simulation.