Accurate X-Ray Absorption Predictions for Transition Metal Oxides: An Advanced Self-Consistent-Field Approach Inspired by Many-Body Perturbation Theory

摘要

Constrained-occupancy self-consistent-field ($\Delta$SCF) methods andmany-body perturbation theories (MBPT) are two strategies for obtainingelectronic excitations from first-principles. Using the two distinctapproaches, we study the O $1s$ core excitations that have become increasinglyimportant for characterizing transition metal oxides and developing theory ofstrong correlations. Interestingly, we find that the $\Delta$SCF approach, inits current single-particle form, systematically underestimates the pre-edgeintensity for chosen oxides, despite its success in weakly correlated systems.By contrast, the Bethe-Salpeter equation within MBPT predicts much betterlineshapes. This inspires us to reexamine the many-electron dynamics of X-rayexcitations. We find that the single-particle $\Delta$SCF approach can berectified by explicitly calculating many-body transition amplitudes, producingX-ray spectra in excellent agreement with experiments. Our study paves the wayto accurately predict X-ray near-edge spectral fingerprints for physics andmaterials science beyond the Bethe-Salpether equation.