Metal oxides are a class of materials with applications in the catalysis and microelectronic domains. Particular attention is nowadays being focused in CaO, which is considered as a prototype oxide from the theoretical point of view, having a wide bandgap (7.1 eV) and a high dielectric constant (11.8) yet unexplored for optoelectronics. Furthermore, 3.125% Ca vacancies in CaO local density approximation band structure calculations predicted a half-metallic ferromagnetic ground state, indicating that CaO could play an important role in the modern field of spintronics as well. CaO crystallizes in the close-packed "rocksalt" structure (Fm3m), and is an ionic material, with some degree of covalence in their bonding. Furthermore, CaO is present in significant amount in the lower mantle of the Earth, therefore being a cheap material with a geophysical interest too.
In the present work, we report the results of an ab initio electronic band structure calculation of cubic CaO based on the Density Functional Theory (DFT) within the Local-Density Approximation (LDA) and the Generalized Gradient Approximation (GGA) frameworks, for the sake of comparison. Geometrical optimization and band structure calculations were performed using the ABINIT code (for information on ABINIT, see http://www.abinit.org). More precisely, the LDA results were obtained using the Perdew-Zunger exchange term, with the Cerpeley-Alder parametrization. On the other hand, the GGA results take into account the Perdew-Burke-Ernzerhof exchange and correlation terms. We optimize the crystal structure, obtaining its band structure, charge density, density of states, and optical properties. The cation Ca and the anion O atoms define a fcc cell, with positions (0,0,0) and (0.5,0.5,0.5), respectively. The basis set plane wave was used with an energy cut-off of 700 eV for geometry optimization, and an energy cut-off of 380 eV for band structure and optical properties calculations (after the geometrical optimization). The difference in the energy cut-off is due to the high computational cost needed for the calculations of electronic properties.
We thank financial support from CNPq-Rede Nanobioestruturas, FAPEMA and FINEP (Brazilian Agencies).
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