JCMsuite has been used in a benchmark study for computing resonances in high-Q cavities. Exponential convergence with finite element degree p is demonstrated to be a valuable measure for reliability of the respective numerical method.
J. R. de Lasson, et al. Benchmarking five numerical simulation techniques for computing resonance wavelengths and quality factors in photonic crystal membrane line defect cavities. Opt. Express 26, 11366 (2018).