Structural and electronic properties of XP4(X = Ru, Os) compounds

By first-principles calculations, here we perform a detailed study on the structural and electronic properties of alpha-, and beta-XP4 (X = Ru, Os) compounds in monoclinic and triclinic symmetry, respectively. Total energy calculations revealed that the beta-XP4 compounds are more stable at the ground state than alpha-XP4 compounds and their dynamical stabilities have been verified by phonon mode analysis. Moreover, structural stabilities at finite temperature are also confirmed through the calculations of the Helmholtz free energy. Electronic band structure calculations show that these XP4 compounds are semiconductors and the band gaps in beta-phases (1.30-1.375 eV) are larger than that in alpha-phases (0.65-0.76 eV), as well as the experimental observations in electrical conductivity. These results provide a systematic understanding of these transition metal phosphides compounds and offer insights into their outstanding structural and electronic properties.