Molecular Dynamics and X-Ray Diffraction Study of Aqueous Beryllium(II) Chloride Solutions

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A structural investigation of a 1.1 molal BeCl2 aqueous solution has been performed by a molecular dynamics simulation together with X-ray diffraction studies of 1.1 and 5.3 molal BeCl2 aqueous solutions at pH =1. A central force model in combination with an improved intramolecular three-body potential was used for water. The ion-water and ion-ion potentials were derived from ab initio calculations. The structure function obtained from the simulation is in satisfactory agreement with that from X-ray diffraction. The MD simulation of the 1.1 molal solution shows that the hydration shell o f Be2+ consists of six water molecules occupying octahedral sites around a central Be2+. The X-ray scattering data of the 5.3 molal solution indicate that Be2+ has only four water molecules in the first hydration shell. The average coordination number of Cl- is found to be about seven in the 1.1 molal solution from both X-ray diffraction and MD simulation, but Cl- is surrounded on the average by 3.4 water molecules in the 5.3 molal solution. The influence of the small divalent Be2+ on the geometry of its nearest neighbour water molecules is compared with the results of previous simulations of 1.1 molal MgCl2 and CaCl2 solutions.