First-principles calculations of the mechanical properties of IrB and IrB2

We have employed ab-initio plane-wave pseudopotential density functional theory to calculate the equilibrium lattice parameters, elastic constants, under the hydrostatic pressures from 0 to 100 GPa for P-1-IrB with Pnma space group and P-5-IrB2 with Pmmn structures. Results show that the P-1-IrB structure is stable, and the incompressibility is enhanced with the increase of pressure. And the elastic constants, bulk modulus, shear modulus for P-5-IrB2 structure exhibit the regular changes under the hydrostatic pressures from 0 to 100 GPa. But when the pressure becomes 50 GPa, the Young's modulus and the lattice constant in the direction b for P-5-IrB2 structure will change exceptionally. Results show that both are not of obvious band gaps in P-1-IrB and P-5-IrB2 electronic structures under zero pressure, because of the covalent effect between Ir and B atoms. The analysis of band structure and the figure of density of states for P-1-IrB and P-5-IrB2 indicate that the two kinds of structure have metal properties.