FDTD Modeling of Nonlocality in a Nanoantenna Accelerated by a CPUCGPU Heterogeneous Architecture and Subgridding Techniques

Contrary to the local response approximation (LRA), the electromagnetic response of subnanometer particles and antennas is influenced by the nonlocal response arising from the free electron spill-out effect. A generalized nonlocal optical response (GNOR) has been successful in explaining the unusual frequency shifts and spectral bandwidth broadening mechanisms, which cannot be captured by LRA models. This article presents a comprehensive finite-difference time-domain (FDTD) implementation of Maxwell-hydrodynamic model with the GNOR term to model the interaction between electromagnetic wave and plasmonic nanoantennas of critical size. Due to the necessity of resolving nonlocal effects with deep subnanometer grid sizes, a subgridding technique becomes crucial for achieving convergence. To this end, a novel heterogeneous CPU-GPU technique is developed to further enhance simulation efficiency. The algorithms are validated on small spherical metallic particles, revealing that the nonlocality effectively eliminates staircasing artifacts at curved interfaces, leading to a higher degree of accuracy compared with local models. In addition, numerical results demonstrate the extended capability of the FDTD method to accurately and efficiently model the blueshift and resonant mode broadening observed in both single nanoantennas and nanodimers. This work contributes significantly to understanding various sophisticated phenomena observed in experiments.