Filtered stress autocorrelation functions of liquid water models

Pressure autocorrelation functions of two models, SPC/E and SPC/Fw, of pure liquid water are presented. Periodic boundary condition simulations, in the microcanonical ensemble (NVE), of 256 molecules at room temperature are accomplished for both models. Green‐Kubo relations are used over the stress tensor time series to extract viscosity properties of the system. Filtering of noise and signal in the numerical data is considered. Three steps are discussed to reach relevant physical data pertaining to transport coefficients calculations: (1) removing noise via Savitzky‐Golay filters to smooth signals, (2) fitting data by combining Kohlrausch type functions, (3) separating low frequency from high frequency behavior. On the latter resides the essential difference between rigid and flexible models. Considerations about the stress tensor structure in flexible case, and the physical meaning each part holds, are explained and used to show similarities in low frequency (librational/translational and cluster) motions present in both models. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011