Fumi-Tosi potential

For MD where the Tosi-Fumi potentials were used, the pressure was 240 MPa and 110 MPa for pure LiCl and the mixture, respeetively. The ealculated temperatures were 957 K and 955 K for pure LiCl and the mixture, respectively. The experimental temperature was 973 K. 

All of the classical force fields used in the study of ionic liquids contain elements of the Tosi-Fumi potential model. Like Eq. (4.2-1), these force fields are all pairwise additive, meaning that the energy and force on an atom can be found by summing all its interactions with its neighbors. In addition, the force fields all contain a Coulomb term that accounts for electrostatic interactions, a short-range repulsive term and one or more long-range attractive (dispersion) terms. 

In all the simulation processes for dissolution and nucleation, the MCY (5), KPC (13), and Fumi-Tosi (15) potentials have been used for water-water, ion—water, and ion-ion interactions, respectively. The time step At has been set at 1.0 fs. The formulae are as follows. 

Fig. 3. Variation with temperature of the diffusion coefficients for various simulated fluids and actual laboratory fluids. Sources of data are, from left to right LJ argon, simulated Refs. 7 (DC) and 12 (C) laboratory. Ref. 41 bard spheres (for which temperature axis corresponds to pV/NkT X.50), Ref. 82 soft spheres. Ref. 20 xenon. Ref. 41 toluene. Ref. 42 methyl cyclohexane. Ref. 43 carbon tetrachloride. Ref. 44 o-terphenyl. Ref. 45 molten KQ, simulated using Tosi-Fumi (TF) potential parameters. Ref. S repellent Gaussian core particles. Ref. 21 (F. H. Stillinger kindly deduced the values his simulation results would infer for argonlike particles in familiar units) Na ions diffusing in molten 6KN03-4Ca(N0j)2 solvent medium. Ref. 46. The dashed extension of lower temperature in the case of xenon is based on the Arrhenius parameters quoted for the data. ...

Another application of the corresponding states approach is that of Abe and Nagashima [259], who used the Tosi-Fumi [112] potential function to obtain the two parameters d = r+ + r for the distance and e for the potential energy. The resulting expression for the fluidity of a molten salts is ... 

An alternative way of calculating defect energies on the basis of static potentials is that outlined by Fumi and Tosi (1957) for alkali halides, in which the energy of the Schottky process is seen as an algebraic summation of three terms ... 

More refined continuum models—for example, the well-known Fumi-Tosi potential with a soft core and a term for attractive van der Waals interactions [172]—have received little attention in phase equilibrium calculations [51]. Refined potentials are, however, vital when specific ion-ion or ion-solvent interactions in electrolyte solutions affect the phase stability. One can retain the continuum picture in these cases by using modified solvent-averaged potentials—for example, the so-called Friedman-Gumey potentials [81, 168, 173]. Specific interactions are then represented by additional terms in (pap(r) that modify the ion distribution in the desired way. Finally, there are models that account for the discrete molecular nature of the solvent—for example, by modeling the solvent as dipolar hard spheres [174, 175]. 

Variables 2 and Zj are charges of ions i and j Ay is the Pauling factor defined as Ay = (1 + zjnx + z-Jn i, where nK and nj represent the numbers of electrons in the outermost shell of ions i and j, respectively Cy = (3/2) aiajEiEj/(Ei + Ej) and dy = (9/4e2)Cy(a, 1/Ar1 + atjE/Nj), where a denotes the polarizability of ions, N is the number of the total electrons of an ion, and E is the first ionization potential, evaluated from the Equation Ef = Nle2h2I Tr2mai for ion i, where h and m are the Planck constant and the mass of the ion, respectively. Values of p, b, and cr are estimated from isothermal compressibilities and thermal expansion coefficients of 17 rock-salt-type crystals of alkali halides by Fumi and Tosi (15). 

Since ion-ion-pair potentials have been thoroughly investigated for rock-salt-type crystals by Tosi and Fumi (15) and those for other type salts have not been as well studied, the MD simulations have been carried out for alkali fluoride and chloride crystals of the rock-salt type NaF, KF, CsF, LiCl, NaCl, and KC1. Due to the limitation of computer times, the simulations have been carried out for only 12 to 20 ps depending on the systems. The experimental conditions for the simulations are summarized in Table II. 

The various parameters needed in these equations come from other work and are given in Table 5.12, taken from Woodcock and Singer. The pairwise potential for potassium chloride, first calculated by Tosi and Fumi in 1964, is reproduced in Fig. 5.12. Typical computational data for an MC calculation are given in Table 5.13. The software of the day generated only 80,000 steps per hour. 

There are several methods for determining ionic radii from physical characteristics of atoms and crystals. Thus, Fumi and Tosi [209] derived ionic radii (similar to the bonded ones) for alkali halides, using the Born model of crystal lattice energy with experimental interatomic distances, compressibilities and polarizabilities. Rossein-sky [210] calculated ionic radii from ionization potentials and electron affinities of atoms, his results were close to Pauling s. Important conclusions can also be drawn from the behaviour of solids under pressure. Considering metal as an assembly of cations immersed into electron gas, its compressibility at extremely high pressures... 

---