The GB-GM-MCTS code is a modified version of the mcts.py code modified for leaf parallelization with a maximum of 25 leaf nodes. The exploration factor is 1/ √ 2 and rollout is terminated if the molecule exceeds the target size as described for GB-GA. Any three-or four-membered alkene rings are subsequently expanded to five-membered rings by inserting C atoms. The reward function is 1 if the predicted J(m) value (see below) is larger than the largest value found so far and 0 otherwise. This reward function was found to work slightly better than the one used by Yang et al. . Table . Maximum J(m) score averaged over 10 runs, the number of molecules evaluated per run, and the required CPU time per run. See text for an explanation of the methods. Results for the non-GB methods are talen from Yang et al. where the number of molecules evaluated per run is estimated based on the average number of molecules generated per minute and the CPU time. The penalized score Following Gómez-Bombarelli et al. and Yang et al. the goal is to maximize J(m):