Density functional theory calculations and crystal structure predictions using the particle swarm optimization method have been combined to determine stable hydrides of lead under pressure. In contrast to other group-IVa hydrides, the stoichiometry PbH6 is the first hydride to become stable, at just under 1 Mbar. For two previously studied stoichiometries PbH4 and PbH8, new energetically favorable phases were identified to become stable around 2 Mbar. In all structures, the hydrogenic sublattices comprises negatively charged H δ− 2 molecules. Competitive PbH4 and PbH6 structures are layered. PbH6 features H2 molecules intercalated between hexagonal close packed Pb-layers, the stable phase of dense pure lead, thus offering a potentially straightforward route towards synthesis. In PbH8, the Pb lattice adapts a beta-Sn structure and hydrogen atoms form quasi-1D-chains. All structures were found to be metallic and to feature superconductivity in their respective stability range, with moderately high Tc in the range 60-100 K for PbH4 and PbH6, and 161-178 K for PbH8.

Binary boron-based compounds are expected to possess unique molecular architecture and chemical bonding. Here, we explore how incorporation of a valence isoelectronic Al atom into boron clusters containing from 10 to 20 atoms modifies the structures and properties of the initial clusters. The global minima structures of neutral and anionic Al-doped boron cluster in the size range from 10 to 20 have been identified using the Crystal structure AnaLYsis by Particle Swarm Optimization method. The states with the promising geometrical structures are reoptimized using density functional theory and tripleζ basis sets. It is found that the geometries of the ground states of the AlB n and AlB n − clusters possess planar, quasi-planar, and exohedral topologies. A nearly circular planar AlB 18 − cluster with C 2v symmetry and a large energy gap 2.98 eV has been discovered. The calculated photoelectron spectra of the anions are well in accord with the experimental spectra. The chemical-bonding analysis suggests that both large HLG and double π-aromaticity have much contribution to the electronic stability of AlB 18 − cluster. Our results elucidate the structural growth behavior of Al-doped boron clusters and enrich the growth pattern and chemical bonding nature of boron-based clusters.

The global-minimum structures of RuBn0/− (n = 9–20) clusters have been determined by the CALYPSO method combined with DFT calculations.