UNIVERSAL BEHAVIOR OF LYAPUNOV EXPONENTS IN UNSTABLE SYSTEMS

We calculate the Lyapunov exponents in a classical molecular dynamics framework. Yukawa and Slater-Kirkwood forces are considered in order to give an equation of state that resembles the nuclear and the atomic He-4 equation of state, respectively, near the critical point for liquid-gas phase transition. The largest Lyapunov exponents lambda are always positive and can be very well fitted near the ''critical temperature'' with a functional form lambda proportional to \T - T-c\(-omega), where the exponent omega = 0.15 is independent of the system and mass number. At smaller temperatures we find that lambda proportional to T-0.4498, a universal behavior characteristic of an order to chaos transition.