Ab initio electronic structures of rhombohedral and cubic HgXO3 (X = Ti, Pb).

First-principles calculations were performed for orthorhombic HgO, rhombohedral and cubic phases of HgTiO(3) (HTO) and HgPbO(3) (HPO). The calculations show that in the rhombohedral phase HTO is a direct gap insulator with a gap of ∼1.6 eV. The rhombohedral phase of HPO, on the other hand, shows a weak metallic character. The results provide an explanation for the electrical properties of these compounds. The cubic phases of HTO and HPO are invariably metallic in nature, thereby suggesting that for HTO the rhombohedral-cubic transition must also be accompanied by a change in the electrical state. Examination of the electronic density of states of these systems revealed no significant on-site mixing of Hg 5d and Hg 6s states in any of these materials.