The QR-BH method reproduced the same PYRPMA crystal energy landscapes, finding all of the same structures as the QR search (see Fig. for P 2 1 ). The space group global energy minima, as well as the experimentally observed crystal structure, are consistently found earlier in the QR-BH searches than QR (Table ). In only two cases was one of the target structures found later in QR-BH than QR, each time for the global minimum in P 2 1 /c at 3000 K, using 2:1 and 10:1 seed:step ratios. However, even in these cases, the mean steps to locate the global minimum was smaller than the steps required in QR. While the improved efficiency of QR-BH over QR is clear, the results do not point strongly to a best set of QR-BH parameters.