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 XSnP2 (X = Zn, Cd and Hg) compounds with chalcopyrite structure were studied using density functional theory. Including the newly predicted HgSnP2, XSnP2 compounds are thermodynamically, mechanically and dynamically stable. The calculated elastic constant, bulk modulus, shear modulus, Young's modulus and Poisson's ratio reveal that XSnP2 compounds are elastic anisotropic: ZnSnP2 is brittle, but CdSnP2 and HgSnP2 are ductile. The XSnP2 compounds are direct-gap semiconductors with band gaps of 2.062, 1.424 and 0.543 eV, respectively. All XSnP2 compounds have strong absorptions and high conductivities in the ultraviolet region. Especially, HgSnP2 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 XSnP2 compounds, the D2d group has five irreducible representations: A1, A2, B1, B2 and E. Modes A1 and A2 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 XSnP2, their thermodynamic properties were also analyzed in detail. The current work deepened the understanding of crystal structures and physical properties of XSnP2 compounds, and will aid in their potential application.