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

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 (alpha-phase; space group Cmmm) and at high pressure it transforms into hexagonal structure (beta-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 alpha- and beta-CaB2 polymorphs have metallic behaviour.