Hydrogen‐Bond Topology and Proton Ordering in Ice and Water Clusters

Singer, Sherwin J.; Knight, Chris

doi:10.1002/9781118135242.ch1

Cited by 20 publications

(21 citation statements)

References 188 publications

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“…In particular, our observations should be useful in shedding light on the complexity behind the origin of the time-dependent infrared dynamics of the proton and hydroxide (32,33). Furthermore, it should also open up interesting discussions for those engaged in understanding PT in ice where phenomena such as proton trapping have also been observed (36). Besides its implications on PT on aqueous systems, the phenomena we observe bear similar features to important biological systems.…”

Section: Resultssupporting

confidence: 53%

Proton transfer through the water gossamer

Hassanali

Giberti

Cuny

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

352

421

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The diffusion of protons through water is understood within the framework of the Grotthuss mechanism, which requires that they undergo structural diffusion in a stepwise manner throughout the water network. Despite long study, this picture oversimplifies and neglects the complexity of the supramolecular structure of water. We use first-principles simulations and demonstrate that the currently accepted picture of proton diffusion is in need of revision. We show that proton and hydroxide diffusion occurs through periods of intense activity involving concerted proton hopping followed by periods of rest. The picture that emerges is that proton transfer is a multiscale and multidynamical process involving a broader distribution of pathways and timescales than currently assumed. To rationalize these phenomena, we look at the 3D water network as a distribution of closed directed rings, which reveals the presence of medium-range directional correlations in the liquid. One of the natural consequences of this feature is that both the hydronium and hydroxide ion are decorated with proton wires. These wires serve as conduits for long proton jumps over several hydrogen bonds.T he mechanism by which protons move through water is at the heart of acid-base chemistry reactions. Understanding the reaction coordinates of this process has been one of the most challenging problems in physical chemistry due to the sheer complexity of water's hydrogen bond network (1-4). Developing a molecular basis for these phenomena is of great relevance in energy conversion applications such as in the design of efficient fuel cells (5). Over 200 y ago, von Grotthuss proposed a mechanism by which water would undergo electrolytic decomposition (6). He imagined that proton conduction involved the collective shuttling of hydrogen atoms along water wires. The early 20th century found many of the great scientists of the time developing conceptual models to understand the properties of water and its constituent ions (7,8). Detailed insights into the mechanisms of proton transfer (PT) came much later from a combination of both ab initio molecular dynamics (AIMD) simulations (3, 9-13) and force-field approaches based on the empirical valence bond formalism (14-16). The current textbook picture of the Grotthuss mechanism that has resulted from these studies involves a stepwise hopping of the proton from one water molecule to the next (1,17,18). This process occurs on a timescale of 1-2 ps. For a successful transfer, the model requires solvent reorganization around the proton-receiving species to develop a coordination pattern like that of the species it will convert to, a process known as presolvation. In all of these characterizations of the Grotthuss mechanism, the role of the connectivity of the water network was not brought to the forefront (3, 19).Sometimes PT has also been thought to take on coherent character involving jumps of several protons simultaneously. In this spirit, Eigen (20) suggested that the proton could delocalize over extended hydrogen...

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Section: Resultssupporting

confidence: 53%

Proton transfer through the water gossamer

Hassanali

Giberti

Cuny

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

352

421

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“…In the actual ice structures there will be variations in the energy due to different hydrogen bonding patterns. 24,25 For large system size and at temperatures at which the H-disordered phases are stable, the crystal structures corresponding to different hydrogen arrangements will form a nearly degenerate energy band, populated almost uniformly. Thus, the idea underlying the calculation of "residual" entropies is that the accessible hydrogen configurations do not correspond to the actual stable phase at T = 0 (which should be ordered), but to an equilibrium H-disordered phase at higher T. This means that small energy differences between different hydrogen arrangements are supposed to not affect significantly their relative weight for the residual entropy, as these arrangements will have nearly the same probability in the (equilibrium) disordered phase.…”

Section: Methods Of Calculationmentioning

confidence: 99%

“…In this context, order-disorder transitions have been observed between several pairs of ice phases. 2,3,25 These transitions are accompanied by an orientational reorganization of water molecules, which turns out to be a kinetically unfavorable rearrangement of the H-bond network.…”

Section: B Actual Ice Networkmentioning

confidence: 99%

Configurational entropy of hydrogen-disordered ice polymorphs

Herrero

Ramı́rez

2014

The Journal of Chemical Physics

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The configurational entropy of several H-disordered ice polymorphs is calculated by means of a thermodynamic integration along a path between a totally H-disordered state and one fulfilling the Bernal-Fowler ice rules. A Monte Carlo procedure based on a simple energy model is used, so that the employed thermodynamic path drives the system from high temperatures to the low-temperature limit. This method turns out to be precise enough to give reliable values for the configurational entropy sth of different ice phases in the thermodynamic limit (number of molecules N → ∞). The precision of the method is checked for the ice model on a two-dimensional square lattice. Results for the configurational entropy are given for H-disordered arrangements on several polymorphs, including ices Ih, Ic, II, III, IV, V, VI, and XII. The highest and lowest entropy values correspond to ices VI and XII, respectively, with a difference of 3.3% between them. The dependence of the entropy on the ice structures has been rationalized by comparing it with structural parameters of the various polymorphs, such as the mean ring size. A particularly good correlation has been found between the configurational entropy and the connective constant derived from self-avoiding walks on the ice networks.

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“…Attempts to calculate the relative stability of Ih and Ic have either relied on empirical force-fields such as TIP4P [26,27] or have lacked an accurate description of anharmonicity [17,28]. TIP4P has since been shown to produce incorrect protonordering energetics and an incorrect static lattice energy difference between Ih and Ic compared to highly accurate diffusion Monte Carlo methods [29]. Moreover, no successful attempts to explain the origin of the greater stability of Ih have been made.…”

Section: Introductionmentioning

confidence: 99%

Anharmonic Nuclear Motion and the Relative Stability of Hexagonal and Cubic ice

2015

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We use extensive first-principles quantum mechanical calculations to show that, although the static lattice and harmonic vibrational energies are almost identical, the anharmonic vibrational energy of hexagonal ice is significantly lower than that of cubic ice. This difference in anharmonicity is crucial, stabilizing hexagonal ice compared with cubic ice by at least 1.4 meV=H 2 O, in agreement with experimental estimates. The difference in anharmonicity arises predominantly from molecular O-H bond-stretching vibrational modes and is related to the different stacking of atomic layers.

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Hydrogen‐Bond Topology and Proton Ordering in Ice and Water Clusters

Cited by 20 publications

References 188 publications

Proton transfer through the water gossamer

Proton transfer through the water gossamer

Configurational entropy of hydrogen-disordered ice polymorphs

Anharmonic Nuclear Motion and the Relative Stability of Hexagonal and Cubic ice

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