First-principles characterisation of structural and electronic properties of some RuO2 crystals

Abstract

Abstract Density functional theory at the level of LDA, GGA, LDA + U, GGA + U and hybrid functionals is applied to investigate structural and electronic properties of three RuO2 crystals. The rutile structure, and the pyrite and flourite modifications of RuO2 are undertaken. The structural properties, enthalpy-pressure curves, electronic states, and Fermi surfaces are presented. The enthalpy-pressure curves show that pressure causes the rutile-RuO2 to transform into pyrite and flourite phases. The pyrtie phase transforms in the fluorite phase. All calculations point out pressure induced rutile → pyrite phase transition in confirmation with the experimental studies. The pyrite → fluorite transition is pointed out by current calculations. The rutile and pyrite crystals are metals while hypothetical fluorite is a semiconductor. All calculations show s that the fluorite has an indirect bandgap in the 0.57–2.96 eV range. The Fermi surface of metallic rutile structure using GGA + U shows improvement over GGA on comparison with the measurement. The GGA + U calculations suggest that rutile → fluorite and pyrite → fluorite metal-insulator transitions are accompanied by orbital ordering.