In order to obtain microcanonical rates from the approximate inverse Laplace transform we optimized thermal instantons at 37 temperatures between 30 K and 2000 K. To ensure convergence with respect to the number of beads, we used 512 beads for temperatures above 300 K and 1024 beads at lower temperatures, where in each case the optimal distribution of beads among reactant and product surface was used, as prescribed in Ref. 63. With this procedure the ring-polymer actions S deviated by no more than 0.01 from the corresponding actions obtained with half as many beads, which implies convergence of the rates to two significant figures. Data generated from the converged instantons is available in the Supporting Information. The data were fitted using convex splines to generate interpolated points and derivatives necessary for the stationary-phase approximation to the inverse Laplace transform as outlined in more detail in the Supporting Information.