Prediction of crystal structure, lattice dynamical, and mechanical properties of CaB2H2

The phase stability of CaB2H2 phase at ambient and high pressures was investigated using the state-of-the-art ab initio program based on density functional theory. At ambient conditions CaB2H2 crystallizes in orthorhombic phase (α-modification; space group Cmc21) and at high pressure it transforms into trigonal structure (β-modification; space group P3¯ m1). From the lattice dynamics simulation and mechanical properties study we have found that the predicted phases are dynamically as well as mechanically stable. The chemical bonding in CaB2H2 is discussed on the basis of electronic structures, charge density, and bond overlap population analysis. In order to verify the possible existence of this compound experimentally we have simulated the Raman, IR spectra and NMR related parameters like isotropic chemical shielding, quadrupolar coupling constant, and quadrupolar asymmetry parameters. The electronic structures reveal that α- and β-CaB2H2 modifications are indirect band gap semiconductor with estimated band gap vary between 0.32 and 1.98 eV.

► The crystal structure of CaB2H2 is predicted.
► Crystal structure of two polymorphs of CaB2H2 has been predicted.
► Electronic, mechanical, optical (Raman, IR and NMR) properties were calculated.
► At 10.8 GPa pressure α-CaB2H2 transform in to trigonal β-phase.
► α- and β-phases are indirect band gap semiconductors.