Ab Initio Molecular Dynamics Investigation of the Electronic and Structural Stability of Anionic O₂^–(H₂O)_n, n = 1–16 Clusters

We report an ab initio molecular dynamics investigation of the electronic and structural stability of water molecules binding to a nucleation O₂^– particle, O₂^–(H₂O)_n with n = 1–16, to ascertain the factors that create particularly stable species. Our results compare well with previous experimental and theoretical reports for clusters with less water content, find three new geometries for species with 7, 9, and 10 water molecules, and determine that 8, 11, 13, and 15 water molecules form remarkably stable structures around O₂^–. These special clusters correspond to well-defined compact structures formed by cubes and four-member rings made of water’s hydrogen bonds interacting with a negative kernel formed by O₂^– with five water molecules, O₂^–(H₂O)₅, in which the negative charge is localized in the first four water molecules, while the fifth molecule provides geometrical stability. We assess the clusters’ energetic stability based on dissociation energies, analyze electron detachment energies to understand its geometrical evolution, and investigate its charge distribution based upon isosurfaces of the highest occupied molecular orbital (HOMO). This research can help provide theoretical insight into the starting steps of nucleation of water clusters around ionic particles.