Fig. shows the low-q behaviour of the structure factor, with and without corrections, as well as the structure factor up to q = 4 Å-1 in the inset. The uncorrected structure factor artificially increases as q goes toward zero, consistent with S v (0; R) from fig. Figure : The performance of the three corrections on the low-q behaviour of the structure factor. The structure factor calculated from the uncorrected RDF artificially increases as q goes toward zero, as a result of the finite-size RDF-sampling. The dashed black curves increase in opacity according to R values going from 30 Å to 50 Å. Note that the Volume-van der Vegt corrections produce results that are almost identical, which means the green curve is hidden behind the blue. 30 Å to 50 Å, showing how the low-q amplitude is entirely dependent on the (arbitrarily) chosen truncation distance. By correcting the RDFs for their finite-sampling, these low-q artefacts can be removed. The van der Vegt-and the volume-corrections are in closest agreement on the q < 0.2 Å-1 signal shape and magnitude, whereas the Perera-correction produces a slightly smaller signal in this region. For these large 100 Å cells, the artificial increase in the uncorrected signal sets in around 2π/(50 Å) = 0.125 Å-1 , with some ringing (i.e. truncation oscillations) present up until ∼0.2 Å-1 . However, not all types of simulation are inexpensive enough to allow cells of these sizes to be employed, making corrections crucial, even at higher q. Especially ab initio molecular dynamics (AIMD) simulations, where the particles are classically propagated from gradients of ab initio potentials , are still too expensive to perform using such large cells. Multiscale methods that couple Quantum Mechanical / Molecular Mechanical (QM/MM) potentials can employ larger (MM) cells , but not without increasing the coupling cost in evaluating the interactions between the two subsystems, and introducing approximations in how the coupling is carried out .