Spectral characterization of hydrogen bond network dynamics in water

Some computational aspects of the characterization of the complex hydrogen bond network dynamics using power spectral analysis are discussed. In the case of hydrogen-bonded liquids, the tagged molecule potential energy is shown to be a useful quantity for capturing the behavior of the networked liquid on different lengths and time scales. The computation of the tagged potential energy for rigid-body effective pair potentials, such as the TIP5P-E and SPC-E models, is discussed. The more structured nature of the TIP5P-E potential, compared to the SPC/E potential, shows up as differences in the high-frequency librational band of the power spectra of the tagged molecule potential energies. The static distributions of the tagged molecule potential energies are also more structured in the case of TIP5P-E, rather than SPC/E, water. The overall behavior of the key power spectral features remains the same in both the models. The possibility of detailed characterization of the power spectrum, and therefore of the underlying dynamics, using a model-based parametric fitting procedure for the power spectra is also discussed. We show that a parametric fitting can allow one to test alternative models of the dynamics underlying the liquid state dynamics.