ReaxFF(MgH) reactive force field for magnesium hydride systems

Area of Science:

• Materials Science
• Computational Chemistry
• Chemical Engineering

Background:

• Developing accurate computational models for materials like magnesium hydride is crucial for understanding hydrogen storage.
• Existing models may not fully capture the complex reactive behavior of magnesium and its hydrides.

Purpose of the Study:

• To develop and validate a reactive force field (ReaxFF(MgH)) for magnesium and magnesium hydride systems.
• To investigate the influence of nanoparticle size on hydrogen desorption kinetics in magnesium hydride.

Main Methods:

• Parameterization of the ReaxFF(MgH) force field using quantum chemical (QM) data for magnesium clusters and condensed phases.
• Validation against QM-derived properties including equations of state, cell parameters, and reaction energies.
• Molecular dynamics (MD) simulations to study hydrogen absorption/desorption in MgH(2) nanoparticles of varying sizes.

Main Results:

• The ReaxFF(MgH) force field accurately reproduces QM data for Mg and MgH(2) phases.
• A clear inverse relationship was observed between MgH(2) nanoparticle size and heat of formation.
• Heat of formation increases as particle size decreases, ranging from -16 to -19 kcal/Mg for 0.6-2.0 nm particles.

Conclusions:

• The developed ReaxFF(MgH) force field is a reliable tool for simulating magnesium hydride systems.
• Nanoparticle size significantly affects the thermochemical properties of MgH(2), with smaller particles exhibiting higher energy.
• These findings have implications for optimizing hydrogen storage materials based on magnesium hydride.