Flexibility and regularity of the hydration structure of a sodium ion. Nonempirical insight

TL;DR

This study uses nonempirical simulations to analyze the structural and energetic properties of sodium ion hydration clusters, revealing how their configurations and coordination numbers vary with size and environment.

Contribution

It provides new insights into sodium hydration structures through nonempirical density functional simulations and molecular dynamics, highlighting the influence of cluster size and configuration.

Findings

Na+ clusters exhibit surface, bulk, and transient configurations.

Coordination numbers typically range from five to six.

Na-O distances depend on structure and local coordination.

Abstract

The stationary nonempirical simulations of Na+(H2O)n clusters with n in a range of 28 to 51 carried out at the density functional level with a hybrid B3LYP functional and the Born-Oppenheimer molecular dynamics modeling of the size selected clusters reveal the interrelated structural and energetic peculiarities of sodium hydration structures. Surface, bulk, and transient configurations of the clusters are distinguished with the different location of the sodium nucleus (close to either the spatial center of the structure or one of its side faces) and its consistently changing coordination number (which typically equals five or six). The <rNaO> mean Na-O distances for the first-shell water molecules are found to depend both on the spatial character of the structure and the local coordination of sodium. The <rNaO> values are compared to different experimental estimates, and the virtual discrepancy of the latter is explained based on the results of the cluster simulations. Different coordination neighborhoods of sodium are predicted depending on its local fraction in the actual specimens.