Quantifying long time memory in phase space trajectories of molecular liquids

A trajectory of liquid water simulated using classical molecular dynamics has been analysed in the framework of symbolic dynamics. The behaviour of symbolic subsequences (words) of nine symbols long has been studied at a very long time of 1 μs. Contrary to naive expectations, the molecular trajectory behaves very differently compared to both a random signal and a random surrogate with spectral properties identical to the molecular trajectory. The molecular system characteristics resemble those of a chaotic map, the Standard map. We conclude that the most probable reason for deviations from randomness in the molecular system is its deterministic dynamics, in particular, the stickiness of periodic islands in the bulk of chaotic motion.