MOLECULAR-DYNAMICS SIMULATION OF LIQUID WATER ALONG THE COEXISTENCE CURVE - HYDROGEN-BONDS AND VIBRATIONAL-SPECTRA

Structure and dynamic properties of liquid water at temperatures betwe en 298 and 523 K and densities between 0.75 and 1.20 g/cm(3) have been investigated by molecular dynamics simulation. A flexible simple poin t charge potential has been asssumed for interactions. The hydrogen bo nding structure in the different simulated states as well as the influ ence of the hydrogen bonds on the dynamic properties (self-diffusion c oefficients, vibrational spectra) is discussed. Special attention is p aid to the intermolecular vibrational spectrum (10-400 cm(-1)). It has been corroborated that the band around 200 cm(-1) can be attributed t o intermolecular O-O stretching vibrations of pairs of H-bonded bounde d molecules. On the contrary, molecular dynamics results indicate that the band close to 50 cm(-1) is independent of the existence of hydrog en 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 stre tching bands as a function of the thermodynamic state are highly corre lated with changes in the percentage of hydrogen bonded molecules. (C) 1996 American Institute of Physics.