Reproducing the FDTD calculation of QNM volume for photonic crystal. Original paper: Kristensen, P. T., C. Van Vlack, and S. Hughes. “Generalized Effective Mode Volume for Leaky Optical Cavities.” Optics Letters 37, no. 10 (May 15, 2012): 1649. https://doi.org/10.1364/OL.37.001649.