Temperature dependence of conductance of the Li+, Cs+, and Clminus;ions in water: Molecular dynamics simulation

摘要

The continuum theory of Hubbardndash;Onsager predicts for the friction coefficient Dgr;zgr; (defined as a difference between friction coefficient and the slip Stokes friction coefficient) the following behavior: Dgr;zgr;0 and part;Dgr;zgr;/part;T0. In case of the Li+ion in water these predictions are confirmed by experiment. In contrast, experimental observations on Cs+and Clminus;ions in water show that at low temperatures Dgr;zgr;0 and part;Dgr;zgr;/part;T0. To explain the observed behavior of Dgr;zgr;(Cs+), the passage through cavities (PTC) mechanism was proposed by Nakaharaetal. The molecular dynamics computer simulation technique was used to find out if the PTC mechanism is responsible for the nonclassical behavior of Dgr;zgr;. No passage through cavities was observed in the computer simulations. Computer simulations were performed on the Li+ion in water, the Cs+ion in water, and the Clminus;ion in water at temperaturesT=268 K andT=298 K. Our results indicate that the observed behavior of Dgr;zgr; for Li+, Clminus;, and Cs+ions is related to the difference in the reorientation times of water molecules in the ion solvation shell and in the bulk.