The sampling efficiency is affected by all parameters used to define the behaviour of the BH trials, in this case including the temperature used for trial acceptance, perturbation cutoffs, the number of parallel seeds and the length of each BH trial. The perturbation cutoff was adjusted so that different types of structural perturbation lead to similar energy changes (Table ). In these initial tests, the temperature was set to 3000K to permit acceptance of increases in energy of up to about 24 kJ/mol according to Boltzmann distribution (lower temperatures are investigated below). Each QR-BH simulation involves 10,000 local lattice energy minimizations generated from 100 parallel BH trials (each started from a different QR seed) and 100 BH steps in each trial. Results of these searches were compared to pure QR structure searches using the same number of energy minimizations in each space group. This length of run is deliberately oversampled to generate better statistics with which to compare the methods; fewer steps are normally required for such simple systems. Because of the stochasticity of the QR-BH process, every simulation (i.e. each molecule + space group combination) was repeated three times and we examine the average and variability of the behaviour between repeats. Since the quasi-random sequence is deliberately deterministic, we used the same initial quasi-random structures in each repeat, but different random seeds for Monte Carlo moves in the BH trials.