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Published February 10, 2005 | metadata_only
Journal Article

ReaxFF_(MgH) Reactive Force Field for Magnesium Hydride Systems


We have developed a reactive force field (ReaxFF_(MgH)) for magnesium and magnesium hydride systems. The parameters for this force field were derived from fitting to quantum chemical (QM) data on magnesium clusters and on the equations of states for condensed phases of magnesium metal and magnesium hydride crystal. The force field reproduces the QM-derived cell parameters, density, and the equations of state for various pure Mg and MgH_2 crystal phases as well as and bond dissociation, angle bending, charge distribution, and reaction energy data for small magnesium hydride clusters. To demonstrate one application of ReaxFF_(MgH), we have carried out MD simulations on the hydrogen absorption/desorption process in magnesium hydrides, focusing particularly on the size effect of MgH_2 nanoparticles on H_2 desorption kinetics. Our results show a clear relationship between grain size and heat of formation of MgH_2; as the particle size decreases, the heat of formation increases. Between 0.6 and 2.0 nm, the heat of formation ranges from −16 to −19 kcal/Mg and diverges toward that of the bulk value (−20.00 kcal/Mg) as the particle diameter increases beyond 2 nm. Therefore, it is not surprising to find that Mg nanoparticles formed by ball milling (20−100 nm) do not exhibit any significant change in thermochemical properties.

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© 2005 American Chemical Society. Received 3 September 2004. Published online 13 January 2005. Published in print 1 February 2005.

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August 19, 2023
August 19, 2023