Molecular dynamics studies on molten alkali hydroxides. II. Rotational and translational motions of ions in molten LiOH

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Abstract
Dynamics of ions in molten LiOH has been investigated by molecular dynamics simulation analyzing the trajectories of the particles. Rotational autocorrelation function of the OH− ion shows rapid and large oscillatory decay at small t as well as rather slow and exponential decay at large t. The function agrees well with that obtained by polarized and depolarized Raman scattering measurements. The former decay was caused by libration of the OH− ion. The latter is based on the reorientation overlapping the relatively frequent libration. It is also found that the exponential decay has a strong correlation with the structural relaxation of the liquid. The OH− ion cannot rotate without any breakdown of the structure of the surrounding ions. Significantly oscillatory translational motions have been demonstrated in terms of various one-particle and ensemble averaged autocorrelation functions. The spectrum analysis elucidated that there exists a strong correlation between the translational motion of the Li+ ion and the rotational and translational motion of the OH− ion. This is in contrast to the case of LiNO3 melt, where Li+ and NO3− ions appear to move independently, at least for the short time oscillatory motion.