Thermodynamic properties of AlH3/AlF3 and MgH2/MgF2 systems as hydrogen storage materials: Acomputational approach

In this work ab initio calculations on AlH3/AlF3 and MgH2/MgF2 are presented. In particular, the full characterisation of computed structural, electronic, vibrational and thermo-dynamic properties has been carried out both on pure compounds and on solid solutions. Several significant reactions have been simulated, such as formation, fluorination and dehydrogenation. The Density Functional Theory has been chosen, considering different Hamiltonians, from pure GGA (PBE) to hybrid (B3LYP), within the periodic CRYSTAL06 code. [1] The calibration of the computational strategy has regarded also the optimization of the basis set, ranging from polarized double- to quadruple-zeta cases. We optimised the computational strategy for the simulation of hydrides and fluorides of light-metals, showing how different choices of computational parameters could affect the characterised properties. Different configurations for solid solutions have been studied, using a newly implemented algorithm in the CRYSTAL code, which allows the classification by symmetry for each H/F ratio. The computed thermodynamic values have shown a fair agreement both with experimental and thermodynamical calculations. These data are relevant to improve our understanding of solid solutions for which only scarce experimental data are available. This work is part of the European FP7 Project FLYHY “Fluorine Substituted High Capacity Hydrides for Hydrogen Storage at low Working Temperatures”. [2] References [1] www.crystal.unito.it [2] www.flyhy.eu