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Microscopic investigation of solvation of selenic acid (H2SeO4) in the aqueous environment has been carried out using the Car-Parrinello molecular dynamics simulation technique. The species deprotonates to HSeO4(-) in a few picoseconds owing to its low pKa1 value of -3.0. A dynamic equilibrium between HSeO4(-) and SeO4(2-), is observed in qualitative agreement with the reported pKa2 value of 1.70. The governing deprotonation mechanism and the structural and dynamic evolutions of the system, particularly the nature of hydrogen bonding, their strengths and lifetimes are investigated comprehensively. A comparison of the vibrational spectra of the species recorded in the gas phase and in the aqueous environment provides further insights on the nature of the interaction between the solute species and water. The results are in good agreement with the available experimental data and other recent computational studies.

The toxicity, mobility, and geochemical behaviors of arsenic are known to vary enormously with its speciation and oxidation states. The present work details results on the basis of ab initio molecular dynamics analysis of various waterborne As-V species, namely, HAsO, HAsO, HAsO, and AsO. The nature of hydrogen bonding of these species with water and its influence on the solvent structure and relaxation behavior are discussed. Useful microscopic insights on the structural and spectroscopic signatures of the species in aqueous media are reported. Comparison of normal-mode frequencies of the species in gas phases to the vibrational density of states in solution provides insights on the influences of solvation and H bonding. The results are compared with the previous experimental and simulation studies, where available.

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An ab initio molecular dynamics investigation is carried out on various water-borne Se(iv) species, HSeO, HSeO and SeO, in aqueous environment. Consistent with the reported acid dissociation constants, in neutral solution HSeO exchanges protons with the surrounding water molecules establishing a dynamic equilibrium with HSeO. The SeO species is found to be stable only in basic environment, which is emulated in the present simulation through introducing a hydroxide ion, OH, in the system. The hydration structure, hydrogen bonding and spectroscopic signatures of the species are comprehensively analyzed. The influence of the solute's hydration structure on the structural and dynamic response of the solvent is discussed. The correlation between the strength as well as the number of hydrogen bonds accepted by the solute on its vibrational properties are analyzed.

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.

Molecular dynamics (MD) is a powerful tool to investigate microscopic transport of atoms and molecules in condensed matter. However, there lies a large class of systems wherein atomic diffusion is...

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