As with the other test systems, we find that the pure QR and QR-BH methods provide essentially the same sets of structures in the low-energy region, as well as in the regions of the important high-energy structures corresponding to the observed polymorphs (Fig. ). To compare efficiency, we examined the minimum steps required to locate each target structure: the four known polymorphs and the global energy minimum (Table ). The QR-BH method consistently required fewer steps to locate the important structures on the landscape at both temperatures. In only one case -polymorph γ in space group P 2 1 -did the pure QR search locate a target structure earlier than QR-BH. The improved efficiency of QR-BH over pure QR searching at locating important high energy structures is somewhat surprising -we expected that basin hopping might favor the lowest energy structures too aggressively, improving the efficiency at finding the global minimum at the expense of sampling the higher energy regions. Our interpretation of these results is that, although α, β, γ and δ are high-energy structures on the whole lattice energy landscape, they correspond to the lowest energy structures within separated local regions of conformational space. Since BH trials begin from different initial structures and explore their local region, these high energy, experimentally observed structures can be located efficiently.