Structural, electronic and mechanical properties of RuO2 from first-principles calculations

The structural, electronic and mechanical properties of ruthenium oxide (IV) (RuO2) in various space groups have been calculated using full-potential linear muffin-tin orbital method. The exchange and correlation potential is treated by local density approximation. The calculated ground state properties, including, lattice constants, internal parameters, bulk modulus and the pressure derivative of the bulk modulus are in good agreement with the available data. This compound is found to undergo a series of structural phase transitions under high pressure. The sequence of the structural phase transition is: rutile→marcasite→pyrite→fluorite that occurs at around 4.92, 22.9 and 100.6 GPa, respectively. The elastic constants Cij for RuO2 in its different structures are calculated using the total energy variation with strain technique. The polycrystalline elastic moduli, namely; shear modulus, Young's modulus, Poisson's ratio, sound velocities and Debye temperature were derived from the obtained single-crystal elastic constants. Band structure calculations show that this compound is a narrow band gap semiconductor with a gap of 0.47 eV in its fluorite structure. While for rutile, marcasite and pyrite structures, this compound exhibits metallic properties.