Structure and dynamics of liquid water

The structure of water is related to the structures of hexagonal boat-form and chair-form ice that exist at atmospheric pressure. The structure may be folded, in three dimensions, to form an icosahedral network, based on the regular arrangement of 14-molecule units. Twenty of the 14-molecule units, comprising in total 280 molecules of water, may form a 3nm diameter icosahedral structures which may be strained with increased size (Doye and Wales, 2001). Icosahedron means a solid figure having twenty faces. The stability of the network is finely balanced, being able to fluctuate between an expanded low density structure and a more dense 

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STRUCTURE AND DYNAMICS OF LIQUID WATER A SHORT REVIEW... 

S.-B. Zhu and G. W. Robinson, Structure and Dynamics of Liquid Water between Plates, J. Chem. Phys. 94 (1991) 1403-1410 references to other simulations of this widely studied system are given in this paper see also E. Spohr, Molecular Dynamics Simulation Studies of the Density Profiles of Water between 9-3 Lennard-Jones Walls, J. Chem. Phys. 106 (1997) 388-391. 

It has recently been pointed out by R0nne et al. [344] that the structure and dynamics of liquid water constitute a central theme in contemporary natural science [345-353]. Modem theoretical considerations are aimed at (a) a detailed description of an electronic structure model of hydrogen bonding, applied to water molecules (see, e.g., Ref. 354), (b) models that involve a certain critical temperature where the thermodynamic response functions of water diverge (see, e.g., Ref. 353), and (c) models that presuppose a coexistence between two liquid phases [344] a low-density liquid phase at the low-pressure side and a high-density liquid phase at the high-pressure side (see also Refs. 355-357). 

Mark, P, Nilsson, L. Structure and dynamics of liquid water with different long-range interaction truncation and temperature control methods in molecular dynamics simulations, J. Comp. Chem. 2002,23(13), 1211-9. 

Models of this kind are employed in molecular dynamics simulations, to determine static and dynamic properties of a given system this permits to verify the consistency and reliability of the model, to explain the molecular origin of physical characteristics of a system or to calculate properties for which no experimental data are available. Great interest has been devoted, for example, to the study of the structure and dynamics of liquid water, ice and solutions. Liquid water simulations are used to represent the hydrogen bond network in the liquid phase and to explain some unusual and not yet understood properties of water, such as its high thermal capacity, in terms of its structure. Still more important is the elucidation of the molecular origin of dynamic phenomenons such as the solvations of ions in water and the interaction of macromolecules with the solvent. 

The method of entropy calculation using both the stmctural and the dynamic information of the system suggests the close relationship between the two in liquids. Generally, when the structural order is larger, the dynamics of the system is slower and vice versa. Thus the structure and dynamics of liquid water are coupled to each other. 

Water is a ubiquitous liquid substance in our world, is essential for life as we know it, and has by all accounts striking properties that set it aside from other liquids. It has therefore been investigated from many points of view and the results have been published in innumerable papers in journals and in many books. Some 70 years ago Dorsey (1940) published a compendium of data on the water substance and Eisenberg and Kauzmann (1969) published a book on the structure and properties of water. A collective set of volumes, edited by Franks (1972) some 40 years ago, was devoted to water and solutions in it. Since then numerous more books and review articles have been devoted to the properties of water, both for itself and as a solvent for various substances, including electrolytes and their constituent ions. The recent review by Malenkov (2(X36) of the structure and dynamics of liquid water covers the developments in these subjects since the earlier books mentioned above. Recent works on the properties of water are the collection of review papers edited by Pratt (2002) and the book by Ben-Naim (2009) on understanding water. 

Malenkov GG (2006) Structure and dynamics of liquid water. J Struct Chem 47 S1-S31 Malenkov GG, Tytik DL, Zheligovskaya EA (2003) Structural and dynamic heterogeneity of computer simulated water ordinary, supercooled, stretched and compressed. J Mol Liq 106 179-198... 

Bakker HJ (2008) Structual dynamics of aqueous salt solutions. Chem Rev 108 1456-1473 Bakker HJ, Kropman MF, Omta AW (2005) Effect of ions on the structure and dynamics of liquid water. J Phys Condens Matter 17 83215-83224... 

Zhu, S.B. and Robinson, G.W. 1991. Structure and dynamics of liquid water between plates. J. Chem. Phys. 94 1403-1410. 

Recently, many experiments have been performed on the structure and dynamics of liquids in porous glasses [175-190]. These studies are difficult to interpret because of the inhomogeneity of the sample. Simulations of water in a cylindrical cavity inside a block of hydrophilic Vycor glass have recently been performed [24,191,192] to facilitate the analysis of experimental results. Water molecules interact with Vycor atoms, using an empirical potential model which consists of (12-6) Lennard-Jones and Coulomb interactions. All atoms in the Vycor block are immobile. For details see Ref. 191. We have simulated samples at room temperature, which are filled with water to between 19 and 96 percent of the maximum possible amount. Because of the hydrophilicity of the glass, water molecules cover the surface already in nearly empty pores no molecules are found in the pore center in this case, although the density distribution is rather wide. When the amount of water increases, the center of the pore fills. Only in the case of 96 percent filling, a continuous aqueous phase without a cavity in the center of the pore is observed. 

Liquid water is an essential component of most terrestrial chemical processes, including those of living organisms. The cooperativity of H-bonding in water clusters is therefore of primary importance for understanding the structure and dynamics of pure water, as well as a vast spectrum of aqueous solvation phenomena in biotic and abiotic systems. In the present section we examine cooperativity effects for a... 

Studies on structure and dynamics of liquids have recently been extended to solvate structure of ions in non-aqueous solutions, and to the structure of complexes with relatively complicated ligands. We can also handle special problems like hydrophobic solvation is. Diffraction studies have been performed on new solvents as e.g. trifluoroethanol [23] and tetramethyl urea [26], and on solvent mixtures [27-30]. More recently the preferential solvation of ions has been subjected by an XD investigation in MgCh-water-methMol ternary systems [31], and the solvation structure around the cations proved to undergo the change of solvent molecules proportionally to the relative concentration of the two solvents. 

In the next section a brief layout of simulation methods will be given. Then, some basic properties of the models used in computer simulations of electrochemical interfaces on the molecular level will be discussed. In the following three large sections, the vast body of simulation results will be reviewed structure and dynamics of the water/metal interface, structure and dynamics of the electrolyte solution/metal interface, and microscopic models for electrode reactions will be analyzed on the basis of examples taken mostly from my own work. A brief account of work on the adsorption of organic molecules at interfaces and of liquid/liquid interfaces complements the material. In the final section, a brief summary together with perspectives on future work will be given. 

Bakker HJ, Skinner JL (2010) Vibrational spectroscopy as a probe of structure and dynamics in liquid water. Chem Rev 110 1498-1517... 

The structure and properties of liquid water are central to the microscopic description and modeling of solvation and thus form a very active area of computational chemistry, with important and often pioneering contributions coming from Clementi and co-workers. In a recent paper Corongiu and Clementi report an analysis of their molecular dynamics simulation studies on liquid water and propose models describing it in terms of solvated water molecules, where a given molecule is at the center of the solvation shell, or in terms... 

Structure and dynamics of water on Pt(lOO) [46,47,127-129], Pt(lll) [62,129,130], and the rigid [131] and liquid [132,133] mercury surface have been investigated. This subject has also been reviewed recently [134]. As an example, I want to briefly discuss the results on the water/mercury interface. 

E. Spohr. Computer simulaton of the structure and dynamics of water near metal surfaces. In G. Jerkiewicz, M. P. Soriaga, K. Uosaki, A. Wieckowski, eds. Solid-Liquid Electrochemical Interfaces, Vol. 656 of ACS Symposium Series. Washington ACS, 1997, Chap. 3, pp. 31-44. 

Xenides D, Randolf BR et al (2005) Structure and ultrafast dynamics of liquid water a quantum mechanics/ molecular mechanics molecular dynamics simulations study. J Chem Phys 122 4506... 

In I960 s the molecular aspect was well introduced to solvents, as well as to solutes, and solution chemistry entered the third period. This period was sometimes called "Renaissance of Solution Chemistry". The structure of water and other liquids was discussed in various ways, and such theoretical considerations were highly supported by the development of high-speed computers. Computer simulation studies appeared as a new way of studying structure and dynamics of solutions. 

The above conclusions were based on calculations and measurements taken from a variety of ices [68]. They offer the prospect of defining a potential for the water molecule that not only satisfactorily reproduces structural data but also generates an acceptable DOS. At present the LR model appears to offer considerable promise in this direction. The local structure of water is often considered to be ice-like and a good model for ice would be an obvious candidate for the structure and dynamics of water. Indeed there are some indications that the two peaks are present in the INS of liquid water, but shifted to lower energies, 24 meV and 32 meV [79]. Therefore, it is appropriate to briefly review the consequences that this model would have for the liquid state of water. Of course this process is by its very nature speculative but it does draw out the intriguing number of unusual properties of water that can be addressed through the Li/Ross model. 

Structure and Ultrafast Dynamics of Liquid Water A Quantum Mechanics / Molecular Mechanics Molecular Dynamics Simulations Study. J. Chem. Phys., 122, 147506. 

One useful discriminator of structure and dynamics in liquid is obtained through entropy. However, experimental or theoretical estimation of the entropy of a liquid confined to a local region is quite hard. This has hampered our understanding of the order/disorder transition in the local region at the mesoscopic length scale. One such rare study concentrated on the estimation of the entropy of water molecules in the groove region and correlated with the observed dynamics. Note that calculation of... 

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