Deviation between experimental and gas-phase conformations. Despite restricting our set to molecules containing no rotatable bonds, this does not preclude molecular flexibility entirely. More complex collective motions cannot be described in terms of a single torsional angle about a covalent bond, and so molecules displaying such conformational flexibility are present in this candidate set -the prototypical example is a ring "flip" or buckling, such as the boat-chair interconversion of cyclohexane rings. As a measure of the typical deviation in molecular geometry between the observed crystal structures and the DFT optimised molecules used in CSP, we present in Figure the histogram of all-atom root-mean-squared deviations (RMSD) in atomic positions between the gas-phase conformers used in CSP and their in-crystal initial conformations as extracted from the CSD.