First-principles study on the structural, electronic, elastic and thermal properties of P42/mnm-BSi

Using first-principles density functional theory, a tetragonal silicon–boron binary structure with space group P42/mnm is predicted in present work. This structure is confirmed to be dynamically and mechanically stable below 19.3 GPa, and possesses lower energy than other candidates. Based on the plane wave pseudopotential method, the electronic structure, elastic constant, bulk modulus, shear modulus, Young's modulus, lattice thermal conductivity and phonon lifetime of P42/mnm-BSi are systematically studied. Interestingly, a four-center and six-electron delocalized π bond is found in P42/mnm-BSi, which is the most important factor for its structural stability. The optical spectra calculations reveal that P42/mnm-BSi is a wide band-gap semiconductor with an indirect band-gap of 2.5 eV and has a promising application in the photoelectric devices. The calculated lattice thermal conductivity along the [001] crystal direction is 145 Wm⁻¹ K⁻¹ that is about three times higher than that along both the [100] and [010] directions, which is originated from the different group velocity along the crystal axis. Moreover, the acoustic–optical coupling has some positive influences on lattice thermal conductivity. This study gives a fundamental understanding of the structural, electronic, elastic and heat transport properties in P42/mnm-BSi. (author)