Ab initio calculations on the structural and lattice dynamical properties of TmX (X=As, P) compounds

The structural and lattice dynamical properties of TmX (X=As, P) compounds were investigated using normconserving pseudopotentials within the generalized gradient approximation correction (GGA) of Perdew–Burke–Ernzerhof (PBE) in the framework of density functional theory (DFT). The structural parameters (a0, B, B′, Ecoh) were determined through total energy and interatomic force minimization and the overall agreement was found to be good. The pressure dependence of the ratios of normalized lattice parameters a/a0, normalized volume V/V0, bulk modulus, elastic constants, Zener anisotropy factor, Poisson's ratio, Young's modulus, shear modulus, and the brittleness were presented and discussed. The thermodynamical properties such as thermal expansion, heat capacity, Debye temperature, and Grüneisen parameter were calculated employing the quasi-harmonic Debye model at different temperatures (0–1000 K) and pressures (0–30 GPa). The phonon dispersion curves and corresponding density of states (DOS) of TmX (X=As, P) were also obtained, and the salient results were interpreted.

► The calculated lattice constants of B1 phase of TmX (X=As, P) are consistent with experimental results.
► The calculated elastic moduli show that TmX (X=As, P) are mechanically stable.
► TmX (X=As, P) are brittle in nature but above 10 GPa they will be ductile.
► Due to the angular character of atomic bonding in TmX (X=As, P), Cauchy pressure is found to be negative.
► The phonon spectra for TmX (X=As, P) are reported.