First-principles study on novel LiB2 phases and superconductivity at ambient pressure

By using the particle swarm optimization (PSO) algorithm implemented in the CALYPSO code, two novel metastable LiB2 structures, namely, P42/mmc-LiB2 and I41/amd-LiB2, were proposed at ambient pressure. Compared with the Cm-LiB2 and AlB2-type P6/mmm-LiB2, the four predicted LiB2 structures are potentially hard materials as indicated by the empirical model formula at atmospheric pressure. The electronic band structure and density of state calculations showed that the conductivities of P42/mmc-, I41/amd-, and P6/mmm-LiB2 were strong, whereas that of Cm-LiB2 was weak. Electron-phonon coupling calculations indicated that the Tc values of P42/mmc-, I41/amd-, and P6/mmm-LiB2 structures were approximately 20.1 K, 12.6 K, and 31.4 K at ambient pressure, respectively. The present results may serve as a reference in the experimental and theoretical study of LiB2 compounds.