Image, charge model

The description of both water-metal and ion-metal interactions by a short-range repulsive potential without significant adsorption energy, augmented by the image charge model of electrostatics, leads to contact adsorption of Br and L and to no adsorption in the case of Li+ and F . CL is a borderline case. 

The image charge model has not been used, because additional assumptions would have to be made for the l -platinum interactions. The total PMFs of the iodine atom and the iodide ion are shown in Fig. 34. 

The field evolved out of the simulation of liquids and solutions and has adopted many of the models from there. Water, ions, and atoms are described by point charge models, augmented by empirical or ab initio short-range and dispersion potentials, the use of which has been validated for the bulk phase. Many models of the interface have been employed, ranging from representations of simple, atomically smooth walls to parametrized interaction potentials from ab initio quantum chemical calculations that describe the interactions with atomic crystals. The metallic character of the solid phase has in most cases been approximated by the image charge model. 

For many electrochemical problems, the models at hand are not adequate. Neither the image charge models nor quantum chemical calculations lead to completely... 

Several simulation studies of the potential of mean force of a single ion near a metal surface have been performed, with image charge models and quantum-chemical models of the metal [202-211]. With the image charge models, only the larger halide ions are contact adsorbed, whereas small ions such as Li+ and F ... 

Image-charge models. These models take into account the discreteness of surface charges, which induces orientation in the adjacent water dipoles [574-577]. Dipoles due to zwit-terionic surface groups, for example, phospholipid headgroups [578], have been also taken into consideration in models of the electrostatic interaction between planar dipole lattices [579-583]. 

The first simulation studies of full double layers with molecular models of ions and solvent were performed by Philpott and coworkers [51,54,158] for the NaCl solution, using the fast multipole method for the calculation of Coulomb interactions. The authors studied the screening of a negative surface charge by free ions in several highly concentrated NaCl solutions. A combination of (9-3) LJ potential and image charges was used to describe the metal surface. 

However, these classical models neglect various aspects of the interface, such as image charges, surface polarization, and interactions between the excess charges and the water dipoles. Therefore, the widths of the electrode/electrolyte interfaces are usually underestimated. In addition, the ion distribution within the interfaces is not fixed, which for short times might lead to much stronger electric helds near the electrodes. 

The electric field or ionic term corresponds to an ideal parallel-plate capacitor, with potential drop g (ion) = qMd/4ire. Itincludes a contribution from the polarizability of the electrolyte, since the dielectric constant is included in the expression. The distance d between the layers of charge is often taken to be from the outer Helmholtz plane (distance of closest approach of ions in solution to the metal in the absence of specific adsorption) to the position of the image charge in the metal a model for the metal is required to define this position properly. The capacitance per unit area of the ideal capacitor is a constant, e/Aird, often written as Klon. The contribution to 1/C is 1 /Klon this term is much less important in the sum (larger capacitance) than the other two contributions.2... 

There are problems with using both of these methods in the simulation of inhomogeneous systems. Because the periodicity of the system is lost in the direction normal to the interface (unless one uses image charges with the flat wall model, which effectively results in a 3D periodic system implementation of the ES method is not straightforward for certain type of systems. Hautman and Klein have presented a modified Ewald sum method for the simulation of systems that are periodic in two... 

In calculating the distribution of image charge aj.x), we use an improved jellium model in which the quasi-potential due to the lattice ions is taken into... 

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