Dynamical Linear Response of TDDFT with LDA+U Functional: strongly hybridized Frenkel excitons in NiO

TL;DR

This paper develops a TDDFT framework with LDA+U functional to study excitons in NiO, revealing hybridization effects and limitations of adiabatic approximations, and emphasizes the need for energy-dependent kernels.

Contribution

It introduces a real-space Wannier function-based TDDFT approach with LDA+U for strongly correlated insulators like NiO, highlighting exciton hybridization and the limitations of adiabatic approximations.

Findings

Strong hybridization of excitons in NiO affects their properties

The adiabatic approximation in TDDFT has significant limitations

Energy-dependent kernels are necessary for accurate exciton modeling

Abstract

Within the framework of time-dependent density-functional theory (TDDFT), we derive the dynamical linear response of LDA+U functional and benchmark it on NiO, a prototypical Mott insulator. Formulated using real-space Wannier functions, our computationally inexpensive framework gives detailed insights into the formation of tightly bound Frenkel excitons with reasonable accuracy. Specifically, a strong hybridization of multiple excitons is found to significantly modify the exciton properties. Furthermore, our study exposes a significant generic limitation of adiabatic approximation in TDDFT with hybrid functionals and in existing Bethe-Salpeter-equation approaches, advocating the necessity of strongly energy-dependent kernels in future development.