Papers by Author: Massimo Celino

Abstract: Hydrogen desorption from hydride matrix is still an open field of research. Extensive abinitio molecular dynamics simulations are performed to characterize the desorption process at the interface MgH2-Mg. The numerical model succesfully repoduces the experimental desorption temperature for the hydride with and without Fe catalyst. Formation energies and work of adhesion are computed and linked to the desorption mechanism. Moreover a detailed analysis of the structural data reveals the role played by the catalysts in the lowering the desorption temperature.

Abstract: We describe two examples of application focusing on first-principles molecular dynamics as an effective tool to unravel the atomic-scale structure of condensed-matter systems. The first application is on disordered network-forming materials and the second is on silicon-doped fullerenes. We show that an accurate modelling of interatomic forces based on density functional theory, when combined with an account of the temperature evolution, is an unavoidable prerequisite for analyzing and interpreting experimental results on a quantitative basis. In the case of disordered systems, we describe the basic structural features of amorphous GeSe4 and highlight the predominant chemical order in this system. The effect of adding or removing an electron charge on the stability of Si-doped fullerenes is exemplified by considering the finite temperature evolution of heterofullerenes.

Abstract: We studied the atomic-level structure of a model Mg-MgH2 interface by means of the Car-Parrinello molecular dynamics method (CPMD). The interface was characterized in terms of total energy calculations, and an estimate of the work of adhesion was given, in good agreement with experimental results on similar systems. Furthermore, the interface was studied in a range of temperatures of interest for the desorption of hydrogen. We determined the diffusivity of atomic hydrogen as a function of the temperature, and give an estimate of the desorption temperature.

Abstract: Extensive electronic structure calculations, based on the density-functional theory, are used to characterize the equilibrium properties and the behaviour under pressure of MgH2. Moreover, substitutional solid solutions for several 3d metals (Fe, Ni, Ti, Al, Pd, Co, etc.) in MgH2 are characterized by computing both relaxed structures and solution energies. Theoretical results are combined with experimental results on samples synthesized by ball milling. MgH2 was milled with 10 wt.% of 3d metals followed by microstructural characterization and hydrogen desorption behaviour. Good correlation between theoretical solution energies and experimental desorption temperatures reveals a general trend in these systems. A few notable exceptions can be detected, which can be explained in terms of peculiarities in the experimental composite microstructure.