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Figure 1
Examining the assumption behind structure factor, S(q), computations. S(q) of our cubic crystal model (lattice parameter a = 3.5 nm, and ten subunit repetitions in each axis) was computed in three ways. We first computed S(q) from a list of subunit point locations [equation (11[link]), blue curve]. The other two structure-factor curves were obtained using equation (12[link]). Initially, the scattered intensity of the same crystal was computed, where the subunits were either symmetric (spheres with a radius of 1.5 nm) or asymmetric (cylinders with a height of 3.2 nm and a radius of 0.17 nm). We then divided each scattering intensity by its subunit form factor: sphere (orange curve) or cylinder (green curve). Except for some discrepancies owing to numerical errors, the difference between the crystal model (blue curve) and the symmetric subunit (sphere – orange curve) graph is minimal, unlike the difference between the crystal model (blue) and the asymmetric subunit (cylinder – green) graphs. The results demonstrate the assumption behind equation (12[link]) stating that the form factor has to come from subunits with spherical symmetry.

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CRYSTALLOGRAPHY
ISSN: 1600-5767
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