First principles electronic structure and band gap pressure coefficient for cadmium-oxide

The static-lattice equation of state (EOS) and electronic energy bands of rocksalt structure cadmium-oxide (CdO) have been calculated for lattice constants ranging from 9.2 to 8.2 bohr, with and without relativistic corrections included, using two distinct density functional theory models; the local density approximation (LDA) and the generalized gradient approximation (GGA). The zero-pressure lattice constants obtained with the LDA and GGA models bracket the measured value. For all models considered here, the fundamental band gap decreases linearly with increasing lattice constant over the full range of the calculations. The calculations with relativistic corrections incorrectly predict that CdO is a metal at ambient conditions, transforming to an insulator under pressure. The nonrelativistic calculations predict insulating behavior for all pressures greater than or equal to zero. The large discrepancies between previous predictions of the energy gap for CdO are shown to be due to model differences, not methodological variations. The predicted pressure coefficient for the fundamental band gap is positive and ranges from 13 to 22 meV/GPa, depending on the model used, with the "best" estimate being 15 meV/GPa. (C) 2007 Wiley Periodicals, Inc.