Supercritical water molecular dynamics simulation

Famulari, A., Specchio, R., Sironi, M., and Raimondi, M. (1998) New basis set superposition error free ab initio MO-VB interaction potential molecular dynamics simulation of water at critical and supercritical conditions, J. Chem. Phys., 108, 3296-3303. 

Molecular dynamics simulation of water at critical and supercritical conditions... 

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. 

Boero M, Parrinello M, Terakura K, Ikeshoji T, Liew CC. (2003) First-principles molecular-dynamics simulations of a hydrated electron in normal and supercritical water. Phys Rev Lett 90 226403-1 to 226403-4. 

P.B. Balbuena, K.P. Johnston and P.J. Rossky, Molecular dynamics simulation of electrolyte solutions in ambient and supercritical water. 1. 

P. B. Balbuena, K. P. Johnston, and P. J. Rossky, Molecular Dynamics Simulation of Electrolyte Solutions in Ambient and Supercritical Water I. Ion Solvation, J. Phys. Chem. 100,2706-2715 (1996). 

S. T. Cui and J. G. Harris, Ion association and liquid structure in supercritical water solutions of sodium chloride a microscopic view from molecular dynamics simulations, Chem. Eng. Sci. 49,2749-2763 (1994). 

M. Boero, M. Parrinello, K. Terakura, T. Ikeshoji, and C. C. Liew (2003) First-Principles Molecular-Dynamics Simulations of a Hydrated Electron in Normal and Supercritical Water. Phys. Rev. Lett. 90, p. 226403... 

A similar approach was used by Johnston, Rossky and coworkers [237-239] who studied the Sj, 2 reaction of methyl chloride with a chloride ion in supercritical water, via molecular dynamics simulations and continuum electrostatic calculations. This work is discussed by Johnston elsewhere in this volume. 

As part of their molecular-based investigation of solvation at supercritical conditions, Chialvo et al. [230] performed molecular dynamics simulations of supercritical electrolyte solutions with three different ion-water models toward the determination of the association constant for the ion pair Na lCF and the equilibrium constant of association between the solvent-separated and the contact... 

Cui, S. T. Harris, J. G. (1994) Ion Association and Liquid Structure in Supercritical Water Solutions of Sodium-Chloride A Microscopic View from Molecular Dynamics Simulations, Chemical Engineering Science 49, 2749-2763... 

Lee, S. H. Cummings, P. T. Simonson, J. M. Mesmer, R. E. (1998) Molecular Dynamics Simulation of the Limiting Conductance of NaCl in Supercritical Water, Chemical Physics Letters 293, 289-294... 

Allen MP, Tildesley DJ (1987) Computer Simulation of Liquids. Oxford University Press, New Yoik Alper HE, Levy RM (1989) Computer simulations of the dielectric properties of water Studies of the simple point chaige and transferable intermolecular potential models. J ChemPhys 91 1242-1251 Balbuena PB, Johnson KP, Rossky PJ (1996a) Molecular dynamics simulation of electrolyte solutions in ambient and supercritical water. 1. Ion solvation. J Phys Chem 100 2706-2715 Balbuena PB, John n KP, Rossky PJ (1996b) Molecular dynamics simulation of electrolyte solutions in ambient and supercritical water. 2. Relative acidity of HCl. J Phys Chem 100 2716-2722... 

Lee SH, Cummings PT, Simonson JM, Mesmer RE (1998) Molecular dynamics simulation of the limiting conductance of NaCl in supercritical water. Chem Phys Lett 293 289-294... 

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)... 

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... 

Some other evidence on the inaccuracy of the NDIS-II results becomes clear by comparing the ab initio molecular dynamics simulation of supercritical water at 7 = 730 K and the NDIS-II data at 7 = 673 K and p = 0.66 g mL . In passing, note that the ab initio approach provides a parametrization-free description of the fluid behavior. The ab initio simulations predicted site-site radial distribution... 

Various equations of state have been developed to treat association ia supercritical fluids. Two of the most often used are the statistical association fluid theory (SAET) (60,61) and the lattice fluid hydrogen bonding model (LEHB) (62). These models iaclude parameters that describe the enthalpy and entropy of association. The most detailed description of association ia supercritical water has been obtained usiag molecular dynamics and Monte Carlo computer simulations (63), but this requires much larger amounts of computer time (64—66). 

Supercritical water (SCW) presents a unique combination of aqueous and non-aqueous character, thus being able to replace an organic solvent in certain kinds of chemical synthesis. In order to allow for a better understanding of the particular properties of SCW and of its influence on the rate of chemical reactions, molecular dynamics computer simulations were used to determine the free energy of the SN2 substitution reaction of Cl- and CH3C1 in SCW as a function of the reaction coordinate [216]. The free energy surface of this reaction was compared with that for the gas-phase and ambient water (AW) [248], In the gas phase, an ion-dipole complex and a symmetric transition... 

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