Valence- and core-level nonlinear optics in solids from real-time TDDFT

Velocity-gauge real-time TDDFT within the generalized Kohn-Sham (GKS) formulation provides a convenient framework for accessing both linear and nonlinear optical response in solids across near-infrared to soft X-ray energy ranges [1, 2]. In this work the GKS TDDFT description of low-order nonlinear response properties such as second harmonic generation and two-photon absorption is investigated in materials like hexagonal BN where excitonic effects are important. Additionally the relevance of this approach to the emerging field of nonlinear X-ray spectroscopy is discussed. Results from TDDFT are compared to benchmark many-body perturbation theory results or experimental data where available.

[1] C. D. Pemmaraju, Computational Condensed Matter 18, e00348 (2019)
[2] C. D. Pemmaraju, New J. Phys. 22 083063 (2020)