We present a first-principles simulation study of vibrational spectral diffusion and hy drogen-bond dynamics in solution of a fluoride ion in deuterated water. The present calculations are based on ab initio molecular dynamics simulation for trajectory genera tion and wavelet analysis for calculations of frequency fluctuations. The O-D bonds of deuterated water in the anion hydration shell are found to have lower stretching frequency than the bulk water. The dynamical calculations of vibrational spectral diffusion for hy dration shell water molecules reveal three time scales: a short-time relaxation (~100 fs) corresponding to the dynamics of intact ion-water hydrogen bonds, a slower relaxation (~7.5 ps) corresponding to the lifetimes of fluoride ion-water hydrogen bonds, and an even longer time scale (~26 ps) associated with the escape dynamics of water from the anion hydration shell. However, the slowest time scale is not observed when the vibrational spectral diffusion is calculated over O-D bonds of all water molecules, including those in the bulk.

The uniformly distributed nanoporous architectures in graphynes have significantly expanded the applicability of the materials of carbon flatland in areas such as water desalination, gas separation, energy storage, catalysis and optoelectronics.

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Droplet spreading at an applied voltage underlies the function of tunable optical devices including adjustable lenses and matrix display elements. Faster response and the enhanced resolution motivate research toward miniaturization of these devices to nanoscale dimensions. The response of an aqueous nanodroplet to an applied field can differ significantly from macroscopic predictions. Understanding these differences requires characterization at the molecular level. We describe the equilibrium and nonequilibrium molecular dynamics simulations of nanosized aqueous droplets on a hydrophobic surface with the embedded concentric electrodes. Constant electrode potential is enforced by a rigorous account of the metal polarization. We demonstrate that the reduction of the equilibrium contact angle is commensurate to, and adjusts reversibly with, the voltage change. For a droplet with O(10) nm diameter, a typical response time to the imposition of the field is of O(10(2)) ps. Drop relaxation is about twice as fast when the field is switched off. The friction coefficient obtained from the rate of the drop relaxation on the nonuniform surface, decreases when the droplet approaches equilibrium from either direction, that is, by spreading or receding. The strong dependence of the friction on the surface hydrophilicity points to the dominance of the liquid-surface friction at the drop's perimeter as described in the molecular kinetic theory. This approach enables correct predictions of trends in dynamic responses associated with varied voltage or substrate material.

The effects of dispersion interaction on the structure, polarity, and dynamics of liquid-vapor interface of a concentrated (5.3M) aqueous NaCl solution have been investigated through first-principles simulations. Among the structural properties, we have investigated the inhomogeneous density profiles of molecules, hydrogen bond distributions, and orientational profiles. On the dynamical side, we have calculated diffusion, orientational relaxation, hydrogen bond dynamics, and vibrational spectral diffusion of molecules. The polarity of water molecules across the interface is also calculated. Our simulation results are compared with those when no dispersion corrections are included. It is found that the inclusion of dispersion correction predicts an overall improvement of the structural properties of liquid water. The current study reveals a faster relaxation of hydrogen bonds, diffusion, and rotational motion for both interfacial and bulk molecules compared to the results when no such dispersion corrections are included. The dynamics of vibrational frequency fluctuations are also calculated which capture the relaxation of hydrogen bond fluctuations in the bulk and interfacial regions. Generally, the hydrogen bonds at the interfaces are found to have longer lifetimes due to reduced cooperative effects.