Polyprismanes are the special type of single-walled nanotubes with an extremely small cross-section in the form of a regular polygon. In the presented study, we considered carbon and silicon polyprismanes that are constructed from carbon and silicon five-, six-, seven- and eight-membered rings, respectively. By means of density functional theory using the periodic boundary conditions, the geometry and electronic characteristics of these tubes were investigated. The results obtained indicate that, with an increase in the effective diameter, carbon polyprismanes undergo an abrupt change in electronic properties, which can be described as a transition from the dielectric to the metallic state. The character of the energy spectrum, as well as the behavior of transmission function near the Fermi level, illustrate that at some critical diameter they begin to exhibit non-typical for the sp³-carbon systems metallic nature. In such a case, it has been found from the partial density of electronic states calculation that the overlapping of bands near the Fermi level is mainly due to the 2p state of carbon atoms. Unlike carbon analogs, silicon polyprismanes are metals for any considered diameter. The metallic properties of the silicon polyprismanes arise due to the 3p states of the silicon atoms. Unexpected properties endowed by the prismane morphology discover new prospects of application of carbon and silicon nanostructures as the basic elements of future electronics.

We studied the hydrogen adsorption on the surface of a covalently bonded bilayer borophene-graphene heterostructure decorated with Pt, Ni, Ag, and Cu atoms. Due to its structure, the borophene-graphene bilayer combines borophene activity with the mechanical stability of graphene. Based on the density functional theory calculations, we determined the energies and preferred adsorption sites of these metal atoms on the heterostructure’s borophene surface. Since boron atoms in different positions can have different reactivities with respect to metal atoms, we considered seven possible adsorption positions. According to our calculations, all three metals adsorb in the top position above the boron atom and demonstrate catalytic activity. Among the metals considered, copper had the best characteristics. Copper-decorated heterostructure possesses a feasible near-zero overpotential for hydrogen evolution reaction. However, the borophene-graphene bilayer decorated with copper is unstable with respect to compression. Small deformations lead to irreversible structural changes in the system. Thus, compression cannot be used as an effective mechanism for additional potential reduction.

We have analyzed the electron, phonon, and superconducting properties of binary hydrides YH6, H3S, YH10, UH10, and CaH10, as compared to the properties of ternary hydride YS4H4using a...