We report first principles molecular dynamics simulations based on the density functional theory and the Car–Parrinello method to study the structures and dynamics of the hydrated Mg²⁺ ion and of the solvated MgHCO₃ ⁺ and MgCO₃ complexes in aqueous solution. According to these simulations, the first hydration shell of the hydrated magnesium ion consists of six water molecules, whereas in the solvated magnesium bicarbonate and magnesium carbonate complexes the Mg²⁺ is mostly five-coordinated, which indicates that when coordinated to magnesium the HCO₃ ⁻ and CO₃ ²⁻ anions reduce its the coordination sphere. Our simulations show that the structures of the most stable monomers of magnesium bi-carbonate and magnesium carbonate in solution are Mg[η¹-HCO₃](H₂O)₄ ⁺ and Mg[η¹-CO₃](H₂O)₄, i.e. the preferred hydration number is four, while the (bi-)carbonate is coordinated to the magnesium in a monodentate mode. The analysis of the exchange processes of the water molecules in the first and second hydration shell of Mg²⁺ shows that the HCO₃ ⁻ or CO₃ ²⁻ ligands affect the dynamics of the magnesium coordination spheres by making its hydration shell more “labile”. Furthermore, molecular dynamics simulations of the non-associated Mg²⁺/Cl⁻ pair in water suggest that, despite negligible differences in the coordination spheres of Mg²⁺, the chloride anion has a significant influence on the water exchange rates in the second hydration shell of Mg²⁺.

Hydroxyapatite (HA), the main mineral phase of mammalian tooth enamel and bone, originates in body fluids from amorphous calcium phosphate (ACP). ACP presents short-range order in the form of small domains with size of 0.9 nm and chemical formula Ca₉(PO₄)₆, known as Posner's clusters. In this study, the aggregation and clustering of calcium and phosphate ions in water has been investigated by means of shell-model molecular dynamics simulations. Calcium phosphate aggregates form in solution with compositions and Ca coordination that are similar to those found in Posner's cluster, but the stoichiometry of these species is dependent on the ionic composition of the solution: calcium-deficient clusters in solutions with low Ca : P ratio; cluster containing protonated phosphate groups in neutral solutions; sodium ions partially substituting calcium in solutions containing a mixture of sodium and calcium ions. These Posner-like clusters can be connected by phosphate groups, which act as a bridge between their central calcium ions. The simulations of the aggregation in solution of calcium phosphate clusters are an unbiased and unequivocal validation of Posner's model, and reveal for the first time the structure and composition of the species that form during the early stages of ACP nucleation at a scale still inaccessible to experiment.

MgO has specific catalysis for CH₄-to-C conversion, and functions as a cost-effective and environmentally friendly template to produce graphene mesosponge with developed porosity, excellent stability, and super soft and elastic properties.

We present an ab initio molecular dynamics study of the alkali metal ions Li⁺, Na⁺, K⁺ and Cs⁺, and of the alkaline earth metal ions Mg²⁺ and Ca²⁺ in both pure water and electrolyte solutions containing the counterions Cl⁻ and SO₄²⁻.

Single-atom catalysts (SACs) on hematite photoanodes are efficient cocatalysts to boost photoelectrochemical performance. They feature high atom utilization, remarkable activity, and distinct active sites. However, the specific role of SACs on hematite photoanodes is not fully understood yet: Do SACs behave as a catalytic site or as a spectator? By combining spectroscopic experiments and computer simulations, we demonstrate that single-atom iridium (sIr) catalysts on hematite (α-Fe₂O₃/sIr) photoanodes act as a true catalyst by trapping holes from hematite and providing active sites for the water oxidation reaction. In situ transient absorption spectroscopy showed a reduced number of holes and shortened hole lifetime in the presence of sIr. This was particularly evident on the second timescale, indicative of fast hole transfer and depletion toward water oxidation. Intensity-modulated photocurrent spectroscopy evidenced a faster hole transfer at the α-Fe₂O₃/sIr/electrolyte interface compared to that at bare α-Fe₂O₃. Density functional theory calculations revealed the mechanism for water oxidation using sIr as a catalytic center to be the preferred pathway as it displayed a lower onset potential than the Fe sites. X-ray photoelectron spectroscopy demonstrated that sIr introduced a mid-gap of 4d state, key to the fast hole transfer and hole depletion. These combined results provide new insights into the processes controlling solar water oxidation and the role of SACs in enhancing the catalytic performance of semiconductors in photo-assisted reactions.