Molecular dynamics simulation of liquid water along the coexistence curve: Hydrogen bonds and vibrational spectra

Abstract

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.

Hydrogen Bond Network of Water around Protein Investigated with Terahertz and Infrared Spectroscopy

“…Thus, this intermolecular stretching is strongly correlated with the neighboring four water molecules (92) and sensitive to the water HB network structure (93). In fact, it is known that temperature increases involve distortion of the tetrahedral HB structure, which induces a slight red-shift and noticeable broadening of this intermolecular stretching vibration mode (62).…”

Hydrogen Bonding and Vibrational Energy Relaxation in Water−Acetonitrile Mixtures

“…The formation of a hydrogen bond between water molecules leads to the red shift of the absorption band of the OH-stretch vibration. 62 Therefore, hydroxyl groups that form a hydrogen bond to acetonitrile have higher frequencies (∼3550 cm -1 , Figure 1a) and, as Figure 6 shows, longer relaxation times. In contrast, hydroxyl groups that make a hydrogen bond to other water molecules have lower frequencies (∼3400 cm -1 ) 62 and much shorter relaxation times.…”

“…62 Therefore, hydroxyl groups that form a hydrogen bond to acetonitrile have higher frequencies (∼3550 cm -1 , Figure 1a) and, as Figure 6 shows, longer relaxation times. In contrast, hydroxyl groups that make a hydrogen bond to other water molecules have lower frequencies (∼3400 cm -1 ) 62 and much shorter relaxation times. Hence, the biexponential decay of the time-resolved pump-probe signal at 3500 cm -1 for intermediate concentrations ( Figure 5) can be attributed to the presence of two types of hydroxyl groups: one bonded and the other not bonded to water molecules.…”

“…The latter value is also consistent with the position (∼3575 cm -1 ) of the non-hydrogen-bonded hydroxyl group in neat water. 5,62 The sum (solid triangles) of two bands corresponding to the water-bonded and non-water-bonded hydroxyl groups correctly describes the linear absorption spectra at the corresponding concentrations (solid curves). Therefore, despite the simplicity of the applied model, it is capable of reproducing the linear absorption spectra as well, which provides strong support for its validity.…”

Water Dynamics at Protein Interfaces: Ultrafast Optical Kerr Effect Study

“…8 The water molecules that solvate the 39 external surface of a protein are also functionally significant; it 40 is known that to fully activate the dynamics and functionality of a 41 protein, 0.40 g of water per gram of protein is required. 9 Because 42 of this importance the hydration layers surrounding peptides, …”