Density Functional Theory Research on the Structure of Active Oxides of RuO2 and IrO2

The optimized bulk modulus, supercell volume and bond length were investigated by a plane-wave pseudopotential density functional theory (DFT) method. In order to compare results of calculations and experiments, the Local Density Approximation (LDA) and the Generalized Gradient Approximation (GGA) methods were used. The results show the data calculated by GGA and LDA are fitted well with those of the equation of state. The calculated energy from LDA is larger than that of GGA, while the supercell volume from LDA is smaller than that of GGA. Further, we found that there's a difference of nearly 50 GPa for the calculated results between LDA and GGA. The bulk modulus, supercell volume, lattice parameter, and bond length calculated from LDA are more accurate than those of GGA. When the coefficient of thermal expansion is introduced to optimize the LDA method of supercell volume calculation, the result will be in good agreement with the experiment.