The Riesz projection method allows to efficently compute the eigenfrequency sensitivities of resonance problems. These are then used to optimize a nano resonator in terms of Q-factor, where the required scattering solutions are computed with the FEM method of JCMsuite.
F. Binkowski, et al. Computation of eigenfrequency sensitivities using Riesz projections for efficient optimization of nanophotonic resonators. Commun. Phys. 5, 202 (2022).