Electronic Excitations in Copper Oxides: Time-Dependent Density Functional Theory Calculations with a Self-Consistent Hybrid Kernel

A theoretical study of the electronic structure and optical response of three copper oxides (Cu2O, Cu4O3, and CuO) in the crystalline state is performed using an all-electron perturbative method based on time-dependent density functional theory. We use hybrid density functional theory to account reliably for the direct and indirect semiconducting nature of these materials, as well as for their magnetic ground state. We consider both global and range-separated standard functionals with empirical Hartree–Fock exchange fractions (B3LYP and HSE06) and functionals in which the fraction of Hartree–Fock exchange is determined from a self-consistent procedure, which requires the calculation of the static dielectric constant in the linear-response approximation. Hybrid exchange is found to be essential to reproduce the experimentally observed optical response of the three oxides. The excited-state calculations yield excellent agreement with experiment for the first optically allowed electronic transitions (with excitonic character) of Cu2O. For Cu4O3, an exciton with a small binding energy can be associated with experimentally observed optical features. In CuO, only one dipole allowed transition is found to contribute to the low-energy region of the optical spectrum.