Theoretical modeling of electronic properties and diffusion in hydrogen-containing boron structures

This study presents a comprehensive analysis of hydrogen behavior in both crystalline and amorphous boron structures using density functional theory (DFT) methods. Starting from the electronic structure of the α - B 96 supercell, we examined the effects of vacancies and hydrogen atoms placed either in interstitials or substitutional positions. The presence of vacancies introduces in-gap states, while hydrogen inserted at a vacancy site tends to passivate the local bonds. The binding energies were found to be around 3 eV, in agreement with previous studies. Hydrogen transport was examined using several techniques: a landscape flooding algorithm (LFA), the breadth-first search (BFS) employed on the states considered in the energy landscape, and also treated as a Markov process, via Master equation. For the crystalline structure, two transport channels were identified, with energies around 0.35 eV and 1.5 eV respectively, thus showing anisotropic transport depending on temperature. In contrast, the amorphous structure presents fewer low-energy paths and predominantly higher diffusion barriers, averaging around 1.4 eV. The diffusion coefficients were estimated from mean squared displacement (MSD) analysis at different temperatures for crystalline and amorphous boron, and the results showed an anomalous diffusion of H in the boron structure. • Crystalline and amorphous boron structures were investigated using DFT calculations. • The relevant potential energy landscape (PEL) is identified. • Diffusion pathways were determined for hydrogen diffusion on the PEL. • In crystalline boron two diffusion channels are revealed. • Anomalous diffusion was observed in both crystalline and amorphous structures.