Investigation of Pressure Dependence of Lattice Dynamical Properties of Potassium Phosphide in Rocksalt Structure using First-Principles Method

Abstract

First-principles calculations have been carried out to investigate the structural stability, lattice dynamical properties, and pressure-dependent phonon behavior of potassium phosphide (KP) in the rocksalt structure. The phonon dispersion relations, phonon density of states (PHDOS), and pressure dependence of phonon frequencies were computed using the linear response approach within the framework of density functional perturbation theory (DFPT). The results reveal that KP is most stable in the rocksalt ferromagnetic phase. The absence of imaginary phonon frequencies at the equilibrium lattice constant confirms its dynamical stability, which is maintained up to a pressure of 2.57 GPa. Furthermore, the phonon frequencies at the high-symmetry points L, Γ, and X exhibit quadratic dependence on pressure, showing an overall increase with compression. The calculated mode Grneisen parameters for the longitudinal optical (LO) and longitudinal acoustic (LA) phonon branches at these points are positive, indicating that the phonon frequencies increase under applied pressure. These findings provide valuable insight into the lattice dynamics and pressure-induced behavior of KP in the rocksalt p