Transitions de phase et propriétés vibrationnelles du matériau LiBeP : Étude ab initio

Abstract

A comprehensive study was conducted on the structural, electronic, vibrational and dielectric properties of the semiconductor compound LiBeP within the framework of density functional theory (DFT). We employed the pseudopotential method, implemented in the ABINIT code. The analysis examined five distinct candidate structural phases (polymorphs): included the cubic phase (AgMgAs), two hexagonal phases (LiGaGe) and (Ni2In), tetragonal phase (Cu2Sb), and orthorhombic phase (MgSrSi). The results of the equation of state showed a very good agreement with the experimental values and confirmed that the tetragonal (Cu2Sb) structure is the most stable. Under pressure, the compound transitions from the tetragonal structure to the orthorhombic structure at 11.43 GPa, and then to the hexagonal structure at 12 GPa. Electrically, in all three phases, the energy gap is indirect. To investigate the vibrational properties, density functional perturbation theory (DFPT) was used in conjunction with the previously mentioned computational method, confirming the dynamical stability of these phases by the absence of imaginary frequencies in the phonon spectra - a finding that was conclusively verified. The dielectric properties revealed that the hexagonal (LiGaGe) structure exhibits the highest dielectric polarization among the studied phases