Ideally, PSO should keep iterating until all particles converge to the global optimal solution instead of stopping at the 15 th generation as in our present case here. However, we found that a number of populations updated their FoM through very large peak shifts and very broad FWHM that included two SLR different peaks. In the Supplementary Figure , we show an example for a population at the 18 th generation. In this case there are two close SLR peaks in both Pd and PdH 0.12 arrays at around 530 nm and 650 nm, respectively. In this case, the algorithm wrongly considered the lower wavelength peak for the case of Pd, and the longer wavelength peak for the case of PdH 0.12 , causing a wrong evaluation of Δλ peak . Furthermore, the FWHM was also calculated for two close SLRs. Consequently, in such case, we cannot correctly calculate the FoM since the parameters originated from two different peaks. Because this similar array began to appear in the 16 th generation, we stopped the PSO after the 15 th generations and confirmed that all the FOM calculated were from single SLR peak (Supplementary Figure ).