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Journal ArticleDOI

Effect of environment on hydrogen bond dynamics in liquid water.

05 Feb 1996-Physical Review Letters (American Physical Society)-Vol. 76, Iss: 6, pp 928-931
TL;DR: It is demonstrated that the long time dynamics of a single hydrogen bond in ambient liquid water is indeed characterized by significant nonexponential relaxation, and this complex relaxation is essentially uncorrelated to the specific bonding patterns near the tagged hydrogen bond.
Abstract: In a series of molecular dynamics calculations we simulate the dynamics of forming and breaking a hydrogen bond in liquid water at room temperature. We show that this dynamics is clearly nonexponential, yet virtually uncorrelated with the fluctuations of neighboring bonds.

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Journal ArticleDOI
14 May 2004-Science
TL;DR: X-ray absorption spectroscopy and x-ray Raman scattering were used to probe the molecular arrangement in the first coordination shell of liquid water and set a strong limit for possible local structure distributions in liquid water.
Abstract: X-ray absorption spectroscopy and x-ray Raman scattering were used to probe the molecular arrangement in the first coordination shell of liquid water. The local structure is characterized by comparison with bulk and surface of ordinary hexagonal ice Ih and with calculated spectra. Most molecules in liquid water are in two hydrogen– bonded configurations with one strong donor and one strong acceptor hydrogen bond in contrast to the four hydrogen– bonded tetrahedral structure in ice. Upon heating from 25°C to 90°C, 5 to 10% of the molecules change from tetrahedral environments to two hydrogen– bonded configurations. Our findings are consistent with neutron and x-ray diffraction data, and combining the results sets a strong limit for possible local structure distributions in liquid water. Serious discrepancies with structures based on current molecular dynamics simulations are observed.

1,278 citations

Journal ArticleDOI
TL;DR: A new flexible simple point-charge water model was derived by optimizing bulk diffusion and dielectric constants to the experimental values via the equilibrium bond length and angle and extensive comparisons of thermodynamic, structural, and kinetic properties indicate that the new model is much improved over the standard SPC model and its overall performance is comparable to or even better than the extended SPC models.
Abstract: In order to introduce flexibility into the simple point-charge (SPC) water model, the impact of the intramolecular degrees of freedom on liquid properties was systematically studied in this work as a function of many possible parameter sets. It was found that the diffusion constant is extremely sensitive to the equilibrium bond length and that this effect is mainly due to the strength of intermolecular hydrogen bonds. The static dielectric constant was found to be very sensitive to the equilibrium bond angle via the distribution of intermolecular angles in the liquid: A larger bond angle will increase the angle formed by two molecular dipoles, which is particularly significant for the first solvation shell. This result is in agreement with the work of Hochtl et al. [J. Chem. Phys. 109, 4927 (1998)]. A new flexible simple point-charge water model was derived by optimizing bulk diffusion and dielectric constants to the experimental values via the equilibrium bond length and angle. Due to the large sensitivities, the parametrization only slightly perturbs the molecular geometry of the base SPC model. Extensive comparisons of thermodynamic, structural, and kinetic properties indicate that the new model is much improved over the standard SPC model and its overall performance is comparable to or even better than the extended SPC model.

1,001 citations

Journal ArticleDOI
TL;DR: In this paper, the authors calculate the mobilities ui of the metal cations Li+, Na+, K+, Rb+, Cs+, and Ca2+ at infinite dilution by molecular dynamics simulation using the SPC/E model for water at 25 °C and a reaction field for the long-range interactions.
Abstract: We calculate the mobilities ui of the metal cations Li+, Na+, K+, Rb+, Cs+, and Ca2+ and the halides F-, Cl-, Br-, and I- at infinite dilution by molecular dynamics simulation using the SPC/E model for water at 25 °C and a reaction field for the long-range interactions. The ion mobilities show the same trends as the experimental results with distinct maxima for cations and anions. The mobilities (defined by ui = Di/kT) of the corresponding uncharged species are also determined by simulation and are in qualitative agreement with Stokes' law. The mobilities of Li+, Na+, K+, Rb+ and F- increase on discharge, whereas Cl, Br, and I have smaller mobilities than the corresponding anions. The mobility of the fictitious I+ ion, which differs from I- only in its charge, lies between that of I- and I in the order uI < uI+ < uI−. The residence time of water in the first solvation shell of small cations (Li+ and Na+) and Ca2+ decreases when the ions are discharged, while the opposite is observed on neutralizing I-, su...

881 citations

Journal ArticleDOI
James C. Phillips1
TL;DR: In this paper, the authors show that the appearance of the stretched exponential is often described in the context of dispersive transport, where is treated as an adjustable parameter, but in almost all cases it is generally assumed that no microscopic meaning can be assigned to even at, a glass transition temperature.
Abstract: Stretched exponential relaxation, , fits many relaxation processes in disordered and quenched electronic and molecular systems, but it is widely believed that this function has no microscopic basis, especially in the case of molecular relaxation. For electronic relaxation the appearance of the stretched exponential is often described in the context of dispersive transport, where is treated as an adjustable parameter, but in almost all cases it is generally assumed that no microscopic meaning can be assigned to even at , a glass transition temperature. We show that for molecular relaxation can be understood, providing that one separates extrinsic and intrinsic effects, and that the intrinsic effects are dominated by two magic numbers, for short-range forces, and for long-range Coulomb forces, as originally observed by Kohlrausch for the decay of residual charge on a Leyden jar. Our mathematical model treats relaxation kinetics using the Lifshitz - Kac - Luttinger diffusion to traps depletion model in a configuration space of effective dimensionality, the latter being determined using axiomatic set theory and Phillips - Thorpe constraint theory. The experiments discussed include ns neutron scattering experiments, particularly those based on neutron spin echoes which measure S( Q,t) directly, and the traditional linear response measurements which span the range from to s, as collected and analysed phenomenologically by Angell, Ngai, Bohmer and others. The electronic materials discussed include a-Si:H, granular , semiconductor nanocrystallites, charge density waves in , spin glasses, and vortex glasses in high-temperature semiconductors. The molecular materials discussed include polymers, network glasses, electrolytes and alcohols, Van der Waals supercooled liquids and glasses, orientational glasses, water, fused salts, and heme proteins. In the intrinsic cases the theory of is often accurate to 2%, which is often better than the quoted experimental accuracies . The extrinsic cases are identified by explicit structural signatures which are discussed at length. The discussion also includes recent molecular dynamical simulations for metallic glasses, spin glasses, quasicrystals and polymers which have achieved the intermediate relaxed Kohlrausch state and which have obtained values of in excellent agreement with the prediction of the microscopic theory.

765 citations

Journal ArticleDOI
TL;DR: Detailed terahertz laser vibration-rotation-tunneling spectra and mid-IR laser spectra are compiled for several isotopomers of small (dimer through hexamer) water clusters to quantify the structures, force fields, dipole moments, and hydrogen bond rearrangement dynamics in these clusters.
Abstract: Extensive terahertz laser vibration-rotation-tunneling spectra and mid-IR laser spectra have been compiled for several isotopomers of small (dimer through hexamer) water clusters These data, in conjunction with new theoretical advances, quantify the structures, force fields, dipole moments, and hydrogen bond rearrangement dynamics in these clusters This new information permits us to systematically untangle the intricacies associated with cooperative hydrogen bonding and promises to lead to a more complete molecular description of the liquid and solid phases of water, including an accurate universal force field

748 citations