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The thermodynamic properties of actinide(III) salt solutions at high concentrations and 25 degree Celsius are explored and a new solution of the binding mean spherical approximation (BIMSA) theory is used to reproduce experimental osmotic coefficient variation with concentration for three binary salt solutions. The molecular dynamics (MD) results are used for discussing the parameters used in the BIMSA.

The development of simple, primitive model descriptions for electrolyte solutions is usually carried out by fitting the system parameters to reproduce some experimental data. We propose an alternative method, that allows one to derive implicit solvent models of electrolyte solutions from all-atom descriptions. We obtain analytic expressions for the thermodynamic and structural properties of the ions, which are in good agreement with the underlying explicit solvent representation, provided that ion association is taken into account. Effective ion-ion potentials are derived from molecular dynamics simulations and are used within a first-order perturbation theory to derive the best possible description in terms of charged hard-spheres. We show that our model provides a valid description for a series of 1-1 electrolytes. [ABSTRACT FROM AUTHOR]

Dipole polarizabilities of a series of ions in aqueous solutions are computed from first-principles. The procedure is based on the study of the linear response of the maximally localized Wannier functions to an applied external field, within density functional theory. For most monoatomic cations (Li+, Na+, K+, Rb+, Mg2+, Ca2+ and Sr2+) the computed polarizabilities are the same as in the gas phase. For Cs+ and a series of anions (F-, Cl-, Br- and I-), environmental effects are observed, which reduce the polarizabilities in aqueous solutions with respect to their gas phase values. The polarizabilities of H(aq)+, OH(aq)- have also been determined along an ab initio molecular dynamics simulation. We observe that the polarizability of a molecule instantaneously switches upon proton transfer events. Finally, we also computed the polarizability tensor in the case of a strongly anisotropic molecular ion, UO22+. The results of these calculations will be useful in building interaction potentials that include polarization effects. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations are used to calculate the exact potential of mean force between charged globular proteins in aqueous solution. The aim of the present paper is to study the influence of the ions of the added salt on the effective interaction between these nanoparticles. The charges of the model proteins, either identical or opposite, are either central or distributed on a discrete pattern. Contrarily to Poisson–Boltzmann predictions, attractive, and repulsive direct forces between proteins are not screened similarly. Moreover, it has been shown that the relative orientations of the charge patterns strongly influence salt-mediated interactions. More precisely, for short distances between the proteins, ions enhance the difference of the effective forces between (i) like-charged and oppositely charged proteins, (ii) attractive and repulsive relative orientations of the proteins, which may affect the selectivity of protein/protein recognition. Finally, such results observed with the simplest models are applied to a more elaborate one to demonstrate their generality. [ABSTRACT FROM AUTHOR]

A multiscale strategy based on the Brownian dynamics (BD) simulation method is presented here. It leads to an approximate but realistic reproduction of the dynamics of charged nanoparticles in suspension. This method is particularly suited to systems containing highly dissymmetric electrolytes with added salts, such as micellar suspensions or protein solutions. The coarse-graining procedure leads to a description where only the translational degrees of freedom of the nanoparticles are left, all the degrees of freedom related to the smallest solutes being rigorously averaged out. The authors’ contribution aims at quantitatively evaluating the influence of the eliminated forces on the dynamics of the nanoparticles. For this purpose, an effective diffusion coefficient has to be calculated. In practice, this effective diffusion coefficient is taken as an input of a coarse-grained simulation that uses the potential of mean force between nanoparticles. The procedure has been validated by the quantitative comparison between the coarse-grained calculations and BD simulations at the “microscopic” level of description (which explicitly include microions). For a model of aqueous solutions of 10-1 electrolyte with a 1-1 added salt, the agreement is found to be excellent. This new method allows us to compute the diffusion coefficients of nanoparticles with a computation time at least one order of magnitude lower than with explicit BD. [ABSTRACT FROM AUTHOR]

We have studied the solubility of potassium fluoride in aqueous solution at near ambient condition, using a simple modeling for the ion and water interactions and computing the values of the chemical potential by molecular dynamics within the framework of Kirkwood generalized thermodynamic integration approach for the evaluation of free energy differences. We report the details of the procedure we used, which is based—at variance with previous attempts—on the individual determination of the chemical potential for the ions in solution. We explore a wide range of salt concentrations up to more than 25 M and determine the solubility. The agreement with the experimental value is reasonable, taking account of the rather crude model used. [ABSTRACT FROM AUTHOR]

Industrial generation of fluorine relies on electrolysis of liquid 2HF/KF solutions. Whereas pure HF has been widely studied experimentally [see, for example, T. Pffeiderer et al., J. Chem. Phys. 113, 3690 (2000)] as well as theoretically [U. Röthlisberger and M. Parrinello, J. Chem. Phys. 106, 4658 (1997)], there is an important lack of description and information at the atomic level for KF solutions in HF. To our knowledge this work is the first attempt to model 2HF/KF at atomic scale by classical molecular dynamics. The model we present here is based on well-tried classical models for pure HF and pure KF. This simple model allows simulation of a system that undergoes a glass-like transition at the experimental transition temperature of 2HF/KF. Furthermore, the clusters spontaneously formed in the liquid give an image of the microscopic structure consistent with previous ab initio studies [T. von Rosenvinge, M. L. Klein, and M. Parrinello, J. Chem. Phys. 107, 8012, 1997)]. Equilibrium proportions between the clusters are computed. Finally, exchange process of molecules between clusters is highlighted, giving deeper insight of the dynamical equilibrium between the clusters. The results presented here are consistent with ab initio simulations cited above and with the sketchy experimental data available on the liquid structure. [ABSTRACT FROM AUTHOR]

The effect of the choice of electrolyte on the separability of different metal ions by pyroprocessing is examined. The studies have shown that the activity coefficients have varied systematically with cation size for a set of trivalent cations.

The computer recreations of mixtures of LiF and the network glass-forming ingredient Be[F.sub.2] are performed to study the correlation between the ionic mobility, viscosity, and the atomic-scale structure. It is observed that the change between the independently diffusing ions in the diluted mixtures to strongly decoupled [Li.sup.+] migration is related to the changing local and intermediate-scale structure in the melts.

The construction of an interaction potential for BeF2 and its mixtures with LiF on a purely first-principles basis is accounted. It is shown that a full aspherical ion (AIM) potential can reproduce the ab inito calculated forces and multipoles for a set of configurations that spanned both tetrahedrally and octahedrally coordinated structures of BeF2 and it is also shown that the potential predicted reasonable behavior for the equation of state for densities close to those of the liquid around melting.

A polarizable ionic interaction potential, constructed from first-principles calculations, was used to analyze the structure, vibrational spectra and transport properties of molten mixtures of LiF and BeF2 across a range of composites. Examination of the structures of the melts revealed the emergence of a slowly relaxing network of BeF4 units as the concentration of BeF2 was increased.

The thermodynamic properties of highly concentrated aqueous solutions of uranyl nitrate at 25 degree Celsius are described. A new resolution of the binding mean spherical approximation (BIMSA) theory, taking into account 1-1 and also 1-2 complex formation, is developed and used to reproduce, from a simple procedure, experimental uranyl nitrate osmotic coefficient variation with concentration.

The predictive capability of the binding mean spherical appproximation (BIMSA) theory is adopted to describe the thermodynamic properties of electrolytes in the case of aqueous solutions of lanthanide(III) nitrate and chloride salts. Concentrated binary solutions of cerium nitrate are prepared in order to measure experimentally water activity and density as a function of concentration.

Osmotic coefficients of aqueous solutions of lanthanide salts are described using the binding mean spherical approximation (BIMSA) model based on the Western formalism for association. An expression for the osmotic coefficient, derived within the BIMSA, is used to fit data for a wide variety of lanthanide pure salt aqueous solutions at 25 degree Celsius.

This study describes the microscopic structure and dynamic properties of potassium fluoride aqueous solutions. This is done using the molecular dynamics simulation method on the basis of Coulomb plus standard Lennard-Jones and Tosi-Fumi ion interactions.

Small-angle neutron scattering experiments were performed at 25 °C on solutions of tetraphenylphosphonium chloride and sodium tetraphenylborate in deuterated water and in deuterated dimethylformamide. The results show a strong attraction between either the organic cations or the organic anions when the salts are dissolved in water. On the contrary, in the organic solvent the attraction between the equally charged organic ions is found to be very weak. This is the first structural evidence of hydrophobic association of small organic ions in water. [ABSTRACT FROM AUTHOR]

The self-diffusion coefficients of N(CH3)(sub 4)(super +) ions in a cation-exchange membrane, the Nafion are measured at different time scales. The radiotracer method confirms the NMR results at long time scales that the diffusion does not depend on electrolyte concentration.