A spin-dependent first-principles investigation of the optoelectronic properties of rare earth zirconates via GWA and the Bethe-Salpeter equation

We have applied many-body perturbation theory to investigate the optoelectronic properties of Ln2Zr2O7 (Ln = La, Ce, Gd, Sm) pyrochlore zirconates starting from spin-dependent density functional theory at the generalized gradient approximation level. Results are intended to explore the relative influence of each lanthanide on the electronic band gap and dielectric properties of pure pyrochlore zirconates. Trivalent lanthanides are modeled with optimized 4f-valence Gaussian-type pseudopotentials to insure the presence of a gapped mean-field ground state. Going beyond DFT, we performed single-shot G0W0 quasi-particle corrections and calculated the excitonic Hamiltonian via the Bethe-Salpeter equation (BSE) to obtain the real and imaginary dielectric function components for each structure using the YAMBO software suite. A double k-grid procedure was applied in order to (1) improve convergence of the optical calculations with respect to k-point sampling and (2) resolve and characterize ground state bound excitons. G0W0 band gap energies of 5.74, 2.65, 4.84, and 4.21 eV were obtained for La2Zr2O7, Ce2Zr2O7, Gd2Zr2O7, and Sm2Zr2O7, respectively. Our BSE results for Sm2Zr2O7 indicate the presence of one or more bound excitons with an energy signature of 1.2 eV.