Structure and dynamic properties of liquid water at temperatures between 298 and 523 K and densities between 0.75 and 1.20 g/cm3 have been investigated by molecular dynamics simulation. A flexible simple point charge potential has been asssumed for interactions. The hydrogen bonding structure in the different simulated states as well as the influence of the hydrogen bonds on the dynamic properties (self-diffusion coefficients, vibrational spectra) is discussed. Special attention is paid to the intermolecular vibrational spectrum (10–400 cm−1). It has been corroborated that the band around 200 cm−1 can be attributed to intermolecular O–O stretching vibrations of pairs of H-bonded bounded molecules. On the contrary, molecular dynamics results indicate that the band close to 50 cm−1 is independent of the existence of hydrogen bonds but depends on the density and temperature of the system. It is suggested that it is simply associated with vibrations of molecules in the cage formed by their neighbors. Shifts of librational and stretching bands as a function of the thermodynamic state are highly correlated with changes in the percentage of hydrogen bonded molecules.

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Molecular dynamics simulations of liquid ethanol at four thermodynamic states ranging from T ) 173 K to T ) 348 K were carried out using the transferable OPLS potential model of Jorgensen (J. Phys. Chem. 1986Chem. , 90, 1276. Both static and dynamic properties are analyzed. The resulting properties show an overall agreement with available experimental data. Special attention is paid to the hydrogen bonds and to their influence on the molecular behavior. Results for liquid ethanol are compared with those for methanol in earlier computer simulation studies.

Molecular dynamics simulations of Na++Na+, Na++Cl−, and Cl−+Cl− ions in dilute aqueous solution were carried out using a flexible single point charge (SPC) model for water. The resulting structural and dynamic properties are compared with experimental data and other computer simulation results. The potentials of mean force [W(r)] between the like ions were determined from constrained molecular dynamics simulations. The resulting W(r) for the Na+–Na+ ion pair is in qualitative agreement with other computer simulation findings, whereas the discrepancies are important in the case of the Cl−–Cl− ion pair. Our Cl−–Cl− mean force potential shows a moderate minimum which does not involve the unexpected strong attraction between chloride ions at short distances as predicted in earlier papers. The solvent structure around the ion pairs for separations corresponding to the maxima and minima of the W(r)’s is analyzed.