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

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.

Thermodynamic analysis of the interaction between metal vacancies and hydrogen in bulk Cu

“…The atomic positions were relaxed to the energy tolerance of 10 À5 eV. In accordance with previous DFT studies on H trapping in transition metals, 21,27 no self-interaction (+U) corrections have been used since, unlike in Cu oxides 40,41 and other transition metal oxides, 42 H at the examined concentrations is not affecting the nature of Cu-Cu bonding.…”

Linear response theories for interatomic exchange interactions

“…We start our analysis of interatomic exchange interactions with either LSDA or GGA picture. It should be noted that the alternative point of view on the electronic structure of CrO 2 and other rutile oxides is based on the LDA + U concept [116,117]. Nevertheless, the situation is probably disputable as many experimental data of CrO 2 are described reasonably well already on the level of LSDA with no clear indications of strong correlations of the Hubbard type [118].…”

A comparison of multilayered coordination numbers in FCC and HCP crystals

“…In [11], computing problems of atom numbers of different coordination shells in cubic crystals were studied. Coordination structure is a basis for the cluster dynamics in mesoscopic modeling technique [12], molecular dynamics simulations for deformation in a metal or alloy [13], density functional theory [14,15], and discontinuous martensitic transition dynamics [16].…”