Novel superconducting structures of BH2 under high pressure

Abstract

The crystal structures of boron hydrides in a pressure range of 50–400 GPa were studied using the genetic algorithm (GA) method combined with first-principles density functional theory calculations. BH₄ and BH₅ are predicted to be thermodynamically unstable. Two new BH₂ structures with Cmcm and C2/c space group symmetries, respectively, were predicted, in which the B atoms tend to form two-dimensional sheets. The calculated band structures showed that in the pressure range of 50–150 GPa, the Cmcm-BH₂ phase has very small gaps, while the C2/c-BH₂ phase at 200–400 GPa is metallic. The superconductivity of the C2/c-BH₂ structure was also investigated, and electron–phonon coupling calculations revealed that the estimated T_c values of C2/c-BH₂ are about 28.18–37.31 K at 250 GPa.