Phase-space invariants as indicators of the critical behavior of nanoaggregates.

A phase-space approach is proposed for molecular dynamics simulations, which serve as a bridge between detailed descriptions of microscopic world and macroscopic properties of matter. The introduction-aside from the angular momentum of spatial rotations-of other "hyperangular" momenta (the overall grand angular momentum of a cluster of particles and those describing the deformation and rearrangement modes) permits one to analyze different degrees of freedom and to extract, from simulation data, a kinetic energy partition in terms of phase-space invariants. Model calculations illustrate how these provide specific signatures of critical behavior, such as energy thresholds for openings of chaotic pathways in small clusters and for phase transitions in nanoaggregates.