First-principles study of the electronic structure, charge density, Fermi surface and optical properties of zintl phases compounds Sr2ZnA2 (A=P, As and Sb)

Abstract

We present first-principles calculations of the electronic structure, Fermi surface, electronic charge density and optical properties of Sr2ZnA2 (A=P, As and Sb) based on density-functional theory using the local density approximation (LDA), generalized-gradient approximation (GGA) and the Engel–Vosko GGA formalism (EV-GGA). Additionally, modified Becke–Johnson (mBJ) is also used to improve the band splitting results. The calculated band structure and density of states show that Sr2ZnA2 compounds are metallic. The total DOS at Fermi level N(EF) is 72.92, 73.06 and 33.47 states/eV and the bare electronic specific heat coefficient (γ) is 12.64, 5.805 and 12.67mJ/mol-K2 for Sr2ZnP2, Sr2ZnAs2 and Sr2ZnSb2, respectively. The Fermi surface of Sr2ZnA2 compounds is composed of two bands crossing along the Γ−A direction of Brillouin zone. There exists a strong hybridization between Zn-p/s and Sb-d, Sb-p and Sr-d and also between Sr-s and Sr-p states. The bonding features are analyzed by using the electronic charge density contour in the (101) crystallographic plane. We found that Sr forms an ionic bond with Zn, whereas Zn forms a strong covalent interaction with P/As/Sb atoms. For further insight information about the electronic structure, the optical properties are derived and analyzed.