Supercritical aqueous solutions molecular dynamics simulation

We now mention two other recent studies whose conclusions are broadly in line with those of Omta et al. (Omta et al., 2003). Guardia et al. (Guardia et al., 2006) carried out extensive molecular dynamics simulations of aqueous alkali metal and halides at ambient and supercritical conditions to explore the effects of ions on the intermolecular connectivity of water in the close vicinity of solutes. From a dynamical perspective, the most relevant feature was that the lifetimes of hydrogen bond do not seem to be affected in an appreciable manner by the presence of ions. More recently, in 2007, Smith et al. (Smith et al., 2007)... 

Driesner, T. (1998) Molecular Dynamics Simulation Study of Ionic Hydration and Ion Association in Dilute and 1 Molal Aqueous Sodium Chloride Solutions from Ambient to Supercritical Conditions, Geochimica et Cosmochimica Acta. In press. 

Driesner T, Seward TM, Tironi IG (1998) Molecular dynamics simulation study of ionic hydration and ion association in dilute and 1 molal aqueous sodium chloride solutions from ambient to supercritical conditions. Geochim Cosmochim Acta, 62 3095-3107 Easteal AJ, Giaquinta PV, March NH, Tosi MP (1983) Chemical effects in diffusion and stracture of zinc chloride in aqueous solution. Chem Phys 76 125-128 Enderby JE, Neilson GW (1983) The stracture of electrolyte solutions. Rept Prog Phys 44 593-653... 

Chialvo, Cochran, Cummings, and their co-workers have extensively studied the solvation of ions in SC water via molecular dynamics simulation (see Supercritical Water and Aqueous Solutions Molecular Simulation) They have observed attractive, weakly attractive, and repulsive solutes, including Na" " and Cl , methanol, and Ar, respectively. A typical plot of the excess number of water molecules found around an Na+ ion as a function of the distance from the ion is shown in Figure 7 for two SC state points. For the more highly compressible state (Pr = 1 -0, T, = 1.05), the Na+ ion is surrounded by, on average, about 25 more water molecules than would be predicted on the basis of the bulk density. The... 

MOLECULAR DYNAMICS SIMULATION OF SUPERCRITICAL AQUEOUS SOLUTIONS... 

In this chapter, we have reviewed some of our own work on solvation properties in supercritical fluids using molecular dynamics computer simulations. We have presented the main aspects associated with the solvation structures of purine alkaloids in CO2 under different supercritical conditions and in the presence of ethanol as co-solvent, highlighting the phenomena of solvent density augmentation in the immediate neighborhood of the solute and the effects from the strong preferential solvation by the polar co-solvent. We have also presented a summary of our results for the structure and dynamics of supercritical water and ammonia, focusing on the dielectric behavior of supercritical water as functions of density and temperature and the behavior of excess solvated electrons in aqueous and non-aqueous associative environments. 

Brownian Dynamics Continuum Solvation Density Functional Theory (DFT), Hartree-Fock (HF), and the Self-consistent Field Monte Carlo Simulations for Complex Fluids Monte Carlo Simulations for Liquids Poisson-Boltzmann Type Equations Numerical Methods Rates of Chemical Reactions Supercritical Water and Aqueous Solutions Molecular Simulation Transition State Theory. 

Several studies have been reported on the determination of the mean-force potential between aqueous ion pairs at ambient conditions, " yet little is known about the speciation in aqueous solutions at near-critical and supercritical conditions " which are typically encountered in technological processes where supercritical water is either the reaction medium or the energy carrier. In this section we analyze the association, equilibrium, and the kinetic (interconversion) rate constants for an infinitely dilute aqueous Na /CI" solution as described by a water-electrolyte model at several supercritical state conditions. In Section 3.3.1 we briefly describe the statistical mechanical formalism for the determination of the thermodynamic constants and the molecular dynamic determination via constraint dynamics. In Section 3.3.2 we discuss the actual kinetics of the inteicon-version between two ion pair configurations leading to the definition of the corresponding equilibrium constant. Finally, in Section 3.3.3 we discuss the outcome of the comparison between the association constants from simulation and... 

The simulation of condensed phase systems by statistical mechanical methods has become a major research area in recent years. Of course, much of this work has been directed toward biologically relevant systems. The contributions in this section of ECC tend toward theory as much as computation and include the articles by Rob Coal son Poisson-Boltzmann Type Equations Numerical Methods), Peter Cummings Classical Dynamics of Nonequilibrium Processes in Fluids), a second article by Cummings Supercritical Water and Aqueous Solutions Molecular Simulation), Brian Laird Interfaces Liquid-Solid), Chi Mak Condensed-... 

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