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Unraveling the Hydration Properties of the Ba2+ Aqua Ion: the Interplay of Quantum Mechanics, Molecular Dynamics, and EXAFS Spectroscopy
journal contribution
posted on 2019-10-18, 18:39 authored by Valentina Migliorati, Alessandro Caruso, Paola D’AngeloThe
structural and dynamic properties of the Ba2+ cation
in water have been studied by combining quantum mechanical (QM) calculations,
molecular dynamics (MD) simulations, and extended X-ray absorption
fine structure (EXAFS) spectroscopy. An effective Ba2+-water
interaction potential, to be used in the MD simulation of a Ba2+ aqueous solution, has been developed by means of QM methods,
and the validity of the whole procedure has been assessed by comparing
the theoretical structural results with the EXAFS experimental data.
By combining distance and angular distribution functions it was possible
to unambiguously identify the geometry adopted by the water molecules
surrounding the ion in the solution. The Ba2+ ion was found
to preferentially form an 8-fold first shell complex with a bicapped
trigonal prism (BTP) geometry. The 8-fold complex is in equilibrium
with a 9-fold structure having a tricapped trigonal prism (TTP) geometry,
and the hydration shell is very diffuse and flexible, being characterized
by a very fast solvent exchange process on the picosecond time scale.