Crystallographic resolution ($d_{\min }$)

Crystallographic resolution describes the spatial detail represented by a diffraction data set and the resulting electron density map. In X-ray crystallography, its conventional numerical measure $d_{\min }$ is the smallest lattice-plane spacing represented by measured reflections. A smaller stated distance means finer nominal resolution.^[ref]

From Bragg's law, first-order diffraction at the largest measured glancing angle ${\theta }_{\max }$ giveswhere $\lambda$ is the X-ray wavelength. For an illustrative wavelength $1\mathring{\mathrm{A}}$ and ${\theta }_{\max }=30^{\circ }$, the nominal resolution is $1\mathring{\mathrm{A}}$. At the same wavelength and a maximum angle of15degrees, it is about $1.93\mathring{\mathrm{A}}$: collecting smaller-angle reflections alone omits finer spatial information.^[ref]

The2000 structure of a bacterial small ribosomal subunit provides a concrete use of the term: its primary report describes refinement to3Å resolution and interprets RNA–protein architecture. That number characterizes the data/model's spatial detail, not an assertion that every atomic coordinate has exactly3Å uncertainty. Noise, missing reflections, directional coverage and model errors still matter.^[ref]