Hydration Structure of ₁₀₂No²⁺: A Density Functional Theory-Molecular Dynamics Study

Abstract

The hydration structure of No 2+ , the divalent cation of nobelium in water, was investigated by ab initio molecular dynamics (MD) simulations. First, a series of benchmark calculations were performed to validate the density functional theory (DFT) calculation methods for a molecule containing a No atom. The DFT-MD simulation of the hydration structure of No 2+ was conducted after the MD method was validated by simulating the hydration structures of Ca 2+ and Sr 2+ , whose behavior was previously reported to be similar to that of No 2+ . The model cluster containing M 2+ (M = Ca, Sr, or No) and 32 water molecules was used for DFT-MD simulation. The results showed that the hydration distance of No 2+ was intermediate between those of Ca 2+ and Sr 2+ . This trend in the hydration distance is in good agreement with the elution position trend obtained in a previous radiochemical experiment. The calculated No−O bond lengths in the optimized structure of [No(H 2 O) 8 ] 2+ was 2.59 Å, while the average No−O bond length of [No(H 2 O) 8 ] 2+ in water by DFT-MD was 2.55 Å. This difference implies the importance of dynamic solvent effects, considering the second (and further) coordination sphere in the theoretical calculation of solution chemistry for superheavy elements.