A homogenous random fractal model for time series produced by constant energy molecular dynamics simulations

Abstract

In the present work we present an analysis of time series of instantaneous temperature and pressure produced during microcanonical (constant energy) molecular dynamics (MD). Simulations were applied to a nickel oxide grain boundary for a temperature range from about 0.15T(m) up to about 0.80T(m), T-m being the melting point of the system. We performed a series of analysis for these time series including test for randomness, power spectrum, Hurst exponent, structure function test and test for multifractality. The obtained results show evidence of an homogenous random fractal model. Pressure time series presents 1/f(alpha) noise over the whole range of frequencies of the system while temperature time series presents a white noise behavior. The origins of this observed behavior are discussed. A comparison also is made with results already obtained from constant temperature MD where the temperature time series present a two-regime behavior: white noise at low frequencies and 1/f(alpha) at high frequencies with alpha increasing as a function of temperature. The origins of this difference in the behavior are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.