Session MM - Chaos and Fractals.
MIXED session, Tuesday afternoon, November 23
Whidbey, Westin Seattle
We study the dynamical behavior of a Lennard-Jones fluid using constant-energy molecular dynamics simulations. The system is studied at several points of the density-temperature phase diagram. Power spectra of instantaneous temperature and pressure show a two-regime power-law 1/f^a behavior. Rescaled range analysis (Hurst test) reveals also this two-regime behavior with strong memory effects for short times and gradual loss of memory at longer times. The dependence of memory on system density and temperature is discussed. By analyzing the Mean Square Displacement (MSD) of the atoms, the two-regime behavior is found to be associated with two kinds of atomic motion: vibrational (high frequency) and diffusional (low frequency). Characteristic times extracted from MSD calculations are in agreement with times deduced from spectral analysis. The system exhibits high-dimensional chaotic dynamics which is difficult to distinguish from stochastic behavior. We calculate the largest Lyapunov exponent of the system and discuss algorithms for the computation of the full Lyapunov spectrum.