Ab initio molecular dynamics investigation on NaCl solution at diluted concentration

Y Ding, COMPUTATIONAL AND THEORETICAL CHEMISTRY, 1153, 25-33 (2019).

DOI: 10.1016/j.comptc.2019.02.012

Despite being one of the simplest and extensively studied systems, the origin of how ions influence water still remains elusive. Many previous studies focused on concentrated solutions, where only limited truly bulk water is present. To gain more insights into the nature of ion-water interactions with the presence of truly bulk water, diluted NaCl solution together with single Na+ and single Cl- solutions are investigated by state-of-the-art ab initio molecular dynamics. Structural, dynamical and electronic properties are studied in some detail. This work revealed that ions do not interrupt the water network in a significant manner under diluted concentration, as shown in almost identical O-O radial distribution functions and angular distributions of water around water in electrolyte solutions and liquid water. Instead, the ions substitute the water molecules in the network and play the role of hydrogen bond donor or acceptor. The influence of ions on water structure and dipole moment is evident in short-range, where different orientational preferences of water are observed and dipole moment distributions tend to shift to smaller values. Compared with results obtained from single ion solutions, no cooperative effect of Na+center dot center dot center dot Cl- ion pair is observed at hundred picosecond time scale. This work also revealed that the water dynamics is strongly related to the void volumes presented in each snapshot, where smaller void volumes resulted in lower water density and ultimately leaded to faster water dynamics.

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