Prediction of structural, lattice dynamical, and mechanical properties of CaB2

Abstract

The structural phase stability of CaB₂ at ground state and high pressures was investigated using state-of-the-art ab initio calculations based on density functional theory. The calculations predicted that at equilibrium conditions CaB₂ crystallizes in an orthorhombic structure (α-phase; space group Cmmm) and at high pressure it transforms into hexagonal structure (β-phase; space group P6/mmm). From lattice dynamics simulation and studies on mechanical properties we have found that the predicted phases are dynamically as well as mechanically stable. The character of chemical bonding in CaB₂ is discussed on the basis of electronic structures, charge density, charge transfer, and bond overlap population analyses. The band structures and density of states reveal that both α- and β-CaB₂ polymorphs have metallic behaviour.