The repeats of QR-BH mostly show comparable behaviour, finding the global minimum with similar efficiency in independent runs starting from the same QR starting points. However, we see greater variability between QR-BH repeats in the cases where the pure QR search was slowest at locating the global minimum. The most extreme case is for benzamide in space group F 2dd, where the pure QR search took 288 steps before the first hit of the global minimum. Two runs of QR-BH showed a big improvement, locating the Table : Steps required to locate the global energy minimum for the single component crystal systems tetracyanoethylene (TCNE), benzamide and glycine in each of 7 space groups (SG), using the quasi-random seeded basin hopping (QR-BH) and quasi-random (QR) methods. For the QR-BH searches, we report the results of each individual run and the mean step number over the three repeats. We also monitored the number of hits to the global minimum energy structure in each system (Table ). For these three molecules, we see small differences between the pure QR and the QR-BH searches, perhaps because their energy landscapes are relatively simple. However, in 15 of the 21 systems, the global minimum is sampled more frequently by QR-BH than QR, reflecting the bias that is introduced towards lowering the energy when local energy minimization of QR structures (the pure QR method) is replaced by a short basin hopping trajectory (as in QR-BH). Thus, despite occasional variability between runs, these initial tests showed the QR-BH algorithm to be stable and efficient at locating the global minimum energy crystal structures, with a moderate improvement over pure QR searching in how quickly it locates the global minimum energy structure. It is also important to reliably locate the possible crystal structures that are slightly higher in energy than the global minimum. As well as the importance of locating high energy polymorphs, the small energy differences often seen between predicted crystal structures means that errors in the model of interaction energies, as well as neglect of thermal vibrations, could lead to mis-ranking and that the true global minimum in free energy is not the global minimum in lattice energy from the energy model used for CSP. Thus, it is important that CSP provides a complete set of low energy structures so that all structures within error of the global minimum have been located. Therefore, we also compare the performance of QR-BH and pure QR searches in sampling the entire low-energy regions of the crystal structure landscapes. Table shows the number of unique crystal structures found in the low energy region (defined as within 5 kJ mol -1 of the global minimum) for each molecule-space group combination for the 10,000 step QR-BH and QR searches. These are compared to a much longer reference search (50,000 QR structures), which should be sufficiently well sampled to locate all low energy structures. These results show only minor differences between methods. Apart from six systems (tetrecyanoethylene in P 2 1 /c; benzamide in space groups P 1, P 2 1 /c, C2/c and F 2dd; and glycine in P 1), the same set of structures is located in all searches, including all three repeats of QR-BH. In three of these cases, the 10,000-minimization QR search misses one of the low energy structures that was located in the longer reference search, and QR-BH finds all of the structures in some or all of the repeats. Glycine in P 1 shows greater differences between searches: the QR search locates only 4 of the 8 low energy structures from the reference search, while QR-BH finds 6, 6 and 5 low energy structures in the three repeats. For only two systems (benzamide in P 1 and C2/c) does the QR-BH perform worse than QR, locating one fewer low energy structure than QR in some of the QR-BH repeats. Figure shows the predicted energy landscape for benzamide in F 2dd. The results demonstrate the reproducibility of the results: QR and QR-BH find nearly identical sets of crystal structures, particularly in the lowest-energy region of the landscapes. Furthermore, the three repeats of QR-BH find the same sets of structures. As expected, as the energy increases away from the global minimum, we observe more structures that are located by QR, but not QR-BH (Fig. , blue dots without corresponding QR-BH hits, or hits in only 1 of the QR-BH repeats). This is because the bias introduced in basin hopping to favor sampling of low energy structures must come at the expense of sampling in the higher energy regions of the landscape. It does not seem that this bias hinders sampling by QR-BH in the usual energy range of polymorphism (typically under 10 kJ mol -1 ), with the parameters used here.