To generate the set of trial structures at each composition we used the Flexible Unit Structure Engine (FUSE), which uses a modular approach to build crystal structures and automatically prevents unphysically close atomic contacts . These are typical of trial structures used to start DFT optimisation calculations for crystal structure prediction, and our aim is to improve them by preoptimising them using SPPs to accelerate access to DFT-optimised structures. For each structure, we performed two types of geometry optimisation calculations: a one-step protocol using DFT starting directly from a generated trial structure, S1, and a two-step protocol where SPPs were used to preoptimise S1 resulting in a new trial structure, S2, which was only then optimised with DFT in a second step (Fig. ). Here the SPP optimisation was done in a fixed unit cell and only atomic positions were allowed to change. Figure shows the mean simulation time to optimise a single structure using a one-step DFT optimisation (S1 → F1, dark-shaded bars) and a two-step protocol (S1 → S2→ F2, light-shaded bars). Due to the additional SPP pre-optimisation step, the mean time for geometry optimisation decreased from the one-to the two-step protocol in all three systems studied: the reduction was 35.3% in Li2Sn2S3Cl4, 28.4% in Li3Si3O5Cl5 and 3.7% in Li4BrOCl. The SPP part of the two-step protocol was ~10 4 times faster than the DFT optimisation part (Fig. ) and made a negligible contribution to the total time to find an equilibrium structure. Figure shows that the SPP optimisation step directs the structures to lower parts of the potential energy surface as the DFT energies of S2 structures are lower than the DFT energies of S1 structures in approximately 90% of the cases. By the time the DFT calculations have fully converged, both the one-step and two-step optimisation protocols access the same energy distributions (Fig. ) in Li4BrOCl, whereas the use of SPP affords more low energy structures at the other two compositions as seen by the shapes of the corresponding energy distributions in Fig. .