MD-Simulation of Molten (Li, K)Cl at the Eutectic Composition. Self-Exchange Velocities of Li- and K-Isotopes near the Cl^--Ions

Abstract

Molecular dynamics simulation (MD) has been done for a molten (Li, K)C1 mixture of the eutectic composition at about 700 K, 950 K and 1100 K and, for comparison, also for pure LiCl and KCl at about 950 K and 1100 K The atomic masses of half the Li + and K + ions have been set at 6.941 and 39.098, respectively. Self-exchange velocities (SEVs) of these cations have been calculated. The Chemla effect is reflected by the SEVs. The isotope effects of the SEVs in the mixture increase slightly with temperature. The motions of the cations with respect to the adjacent CI" are classified into four modes: (1) an oscillating motion, (2) a leaving motion, (3) a wandering motion and (4) a coming-back motion. It is found that the velocity of the leaving motion is dependent only on the masses and the temperature, and independent of the kind of cations and the composition.

A New Analysis of Internal Cation Mobilities in the Molten Binary System (Li, K)Cl

“…It has been previously analyzed by MD simulations for the separating motion of several individual cations from their reference Cl − ion in the present system ( x K = 0.417) . A cation oscillates around the reference anion during an extended time and then suddenly moves away, although in some occasions it may come back soon.…”

“…In other words, the L-process seems to proceed without surmounting a potential barrier. The average velocity of the separating motion is determined mainly by the frequency of the occurrence of the L-process, in other words, by the duration of the O-process; the average velocity has been named the self-exchange velocity (SEV), which has been found to be closely correlated with the (experimentally measured and calculated) internal mobility. ,, …”

“…It has been previously analyzed by MD simulations for the separating motion of several individual cations from their reference Clion in the present system (x K ) 0.417). 31 A cation oscillates around the reference anion during an extended time and then suddenly moves away, although in some occasions it may come back soon. These motions have been classified into the oscillating process (O-process), the leaving-process (Lprocess), and the coming-back process (C-process), respectively.…”

“…The average velocity of the separating motion is determined mainly by the frequency of the occurrence of the L-process, in other words, by the duration of the O-process; the average velocity has been named the self-exchange velocity (SEV), 32 which has been found to be closely correlated with the (experimentally measured and calculated) internal mobility. 29,31,32 Since, in Figure 11, the Coulombic interaction between the cation, M + , and the reference anion, Cl -R , is so strong, the M + cannot move away from Cl -R because of the kinetic energy alone without the presence of another attracting anion. Therefore, in the dynamic dissociation model the role of the attracting anion is regarded as essential.…”