Diborane (${\mathrm{B}}_2{\mathrm{H}}_6$), a high energy density material, was believed to be stable in a wide $P$, $T$ interval. A systematic investigation of the B-H system using the ab initio variable-composition evolutionary simulations shows that boron monohydride (BH) is thermodynamically stable and can coexist with solid B, ${\mathrm{H}}_2$, and ${\mathrm{B}}_2{\mathrm{H}}_6$ in a wide pressure range above 50 GPa. ${\mathrm{B}}_2{\mathrm{H}}_6$ becomes unstable and decomposes into the Ibam phase of BH and ${\mathrm{H}}_2$ ($C2/c$) at 153 GPa. The semiconducting layered Ibam structure of BH at 168 GPa transforms into a metallic phase with space group $P6/mmm$ and a 3D topology with strong B-B and B-H covalent bonds. The Ibam-$P6/mmm$ transformation pathway suggests the possibility of obtaining the metastable Pbcm phase on cold decompression of the $P6/mmm$ phase. The electron-phonon coupling calculations indicate that $P6/mmm$-BH is a phonon-mediated superconductor with a critical temperature of superconductivity ($T_c$) of 14.1–21.4 K at 175 GPa.

To investigate the H2 purification mechanism of V membranes, we studied the adsorption, dissociation, and diffusion properties of H in V, an attractive candidate for H2 separation materials. Our results revealed that the most stable site on the V (1 0 0) surface is the hollow site (HS) for both adsorbed H atoms and molecules. As the coverage range increases, the adsorption energy of H2 molecules first decreases and then increases, while that of H atoms remains unchanged. The preferred diffusion path of atoms on the surface, surface to first subsurface, and first subsurface to second subsurface is HS → bridge site (BS) → HS, BS → BS, and BS → tetrahedral interstitial site (TIS) → BS, respectively. In the V bulk, H atoms occupy the energetically favourable TIS, and diffuse along the TIS → TIS path, which has a lower energy barrier. This study facilitates the understanding of the interaction between H and metals and the design of novel V-based alloy membranes.

The stable crystal structure of LiBeH3 is predicted on the basis of ab initio total-energy calculations using density-functional theory and an extended database of candidate structures and using global optimizations based on an evolutionary algorithm. At the level of density-functional theory, a CaSiO3_1-type structure with space group P21/c, containing BeH4 tetrahedra linked in chains, is the ground-state structure of LiBeH3 (α-LiBeH3). It is found to be lower in energy than the structures proposed in previous studies. The analysis of the electronic structure shows that α-LiBeH3 is an insulator with a band gap of about 4.84 eV and exhibits strong covalent bonding in the BeH4 tetrahedral complexes. Calculations at finite temperatures and high pressures suggest that at T=408 K and ambient pressure a structural transition from α-LiBeH3 (CaSiO3-type) to a YBO3-type structure with space group Cmcm occurs and that at a pressure of 7.1 GPa α-LiBeH3 undergoes a pressure-induced structural transition from the α-phase to a MgSiO3-type structure with space group C2/c. The calculated enthalpies of formation (−45.36 and −30.12 kJ/mol H2 without and with zero-point energy corrections) are in good agreement with the experimental result, indicating that LiBeH3 is a potential hydrogen storage material with low activation barriers for hydrogen desorption.