First-principles studies of structural, elastic, electronic, optical and lattice dynamical properties of XSnP2 (X = Zn, Cd and Hg) compounds

Abstract The structural, elastic, electronic, optical, lattice dynamical and thermodynamic properties of X SnP 2 ( X  = Zn, Cd and Hg) compounds with chalcopyrite structure were studied using density functional theory. Including the newly predicted HgSnP 2 , X SnP 2 compounds are thermodynamically, mechanically and dynamically stable. The calculated elastic constant, bulk modulus, shear modulus, Young's modulus and Poisson's ratio reveal that X SnP 2 compounds are elastic anisotropic: ZnSnP 2 is brittle, but CdSnP 2 and HgSnP 2 are ductile. The X SnP 2 compounds are direct-gap semiconductors with band gaps of 2.062, 1.424 and 0.543 eV, respectively. All X SnP 2 compounds have strong absorptions and high conductivities in the ultraviolet region. Especially, HgSnP 2 has the greatest absorption coefficient and conductivity in the visible region, indicating that it has the strongest visible-light absorption capacity and the best photovoltaic activity. For X SnP 2 compounds, the D 2 d group has five irreducible representations: A 1 , A 2 , B 1 , B 2 and E. Modes A 1 and A 2 only involve displacements of P atoms, but the other three modes involve vibrations of X , Sn and P atoms. Based on the calculated phonon spectra of X SnP 2 , their thermodynamic properties were also analyzed in detail. The current work deepened the understanding of crystal structures and physical properties of X SnP 2 compounds, and will aid in their potential application.