Phase diagrams of alkali halides using two interaction models: A molecular dynamics and free energy study

Abstract

Phase diagrams for potassium and sodium chlorides are determined by molecular dynamics and free energy calculations. Two rigid-ion interaction models, namely, the Born-Mayer-Huggins (BMH) and Michielsen-Woerlee-Graaf (MWG) effective pair potentials, have been used. The critical and triple point properties are discussed and compared with available experimental and simulation data. The MWG model reproduces the experimental liquid-gas equilibria better than the BMH model, being the accordance very good in the lowest temperature region of the coexistent liquids, particularly for NaCl. However, both models underestimate the critical temperatures of KCl and NaCl. Relatively to the solid-gas equilibria, the models do not reproduce well the experimental data. As for the solid-liquid coexistences either the BMH or the MWG models appear unrealistic.

Modeling Solute Thermokinetics in LiCI-KCI Molten Salt for Nuclear Waste Separation

“…The free energy computed by the 2PT method (circles) and coupling TI method [18] (squares) shown in Figure 3.9confirm the accuracy of the 2PT method against a well-established method; the relative error between the predictions is typically less than 1%. Unlike the coupling TI method, the 2PT method requires only modest computing time to derive the free energy with comparable precision.…”

“…Absolute free energy has been computed by Rodrigues and Fernandes using a coupling TI method using the BHM potential [18]. The Einstein crystal method is used to compute the absolute free energy of the solid state, while a two-step procedure is employed for the liquid state.…”

“…Next the Gaussian potential is converted into a null potential to transition into the ideal gas reference state with known thermodynamic properties. For the liquid states, checks have been made to ensure that the TI paths are reversible and no phase change occurs along them [18]. Comparison of absolute (molar) free energy of molten KCl from the 2PT and TI [18] methods at a temperature of 1100 K and a density of 20 nm -3 .…”

“…Thermodynamic integration (TI), which is the method of choice for a variety of applications [11,14,[16][17][18][19], especially with molecular dynamics (MD) simulations, may not be the most optimal choice for nuclear reprocessing applications given the inordinate number of species that are targeted for separation. In several instances, TI can be limited by the optimal choice of the integration path that is not known a priori, and is also constrained in having a reverse path that implicitly excludes a first order phase change.…”

Direct Calculation of Concentration-Dependent Activity Coefficient of UCl3in Molten LiCl-KCl

“…14 The first step is to transform the potential of the solution to Gauss potential with repulsive barrier set close to that of original potential and then calculate the free energy difference F 1 . Gauss potential can be written as: [14] where α and δ are parameters, r is distance between two particles. The second step is to transform the Gauss potential to the null potential of ideal gas and calculate the free energy difference F 2 .…”