Hydration Properties of HPO₄ (n = 0-3) From Ab Initio Molecular Dynamics Simulations

For a comprehensive and detailed microscopic understanding of the hydration properties of primary aqueous phosphorus species of valence states V (viz., H₃PO₄, H₂PO₄^-, HPO₄^2-, and PO₄^3-), a series of extensive ab initio molecular dynamics simulations is conducted at ambient temperature. In each of these cases, the spatially resolved, three-dimensional hydration shells are computed, allowing for a direct microscopic visual understanding of the hydration shells around the species. Since these species are excellent agents for the formation of hydrogen bonds (H-bonds) in water, which determine a wide range of their structural, dynamic, and spectroscopic features, a detailed analysis of the qualitative and quantitative aspects of the H-bonds, including their lifetime calculations, is performed. Vibrational density of states (VDOS) is calculated for each of the species in solute phases, resolved for each H-bonding site, and compared against the gas-phase normal modes of H₃PO₄ for the purpose of understanding the signatures of the peaks in VDOS plots and, in particular, the effects of solvation and H-bonding mechanisms. The results are well in line with available experimental data and other recent computer-aided studies in the literature.