Crystallographic

Crystallographic refers to crystallography, the science concerned with determining the arrangement of atoms in crystalline materials. Crystals exhibit long-range order, with atoms occupying repeating positions within a unit cell that tiles space via a lattice. The primary experimental signature of structure is diffraction of waves by the crystal, most commonly X-rays, but neutrons and electrons are also employed.

The foundational principle is Bragg's law, nλ = 2d sin θ, which connects the wavelength to the spacing of crystal planes. Structural determination combines diffraction data with mathematical methods to locate atomic positions and refine a model. Phase information is not directly observed; methods to recover phases yield electron density maps through Fourier synthesis.

Crystallography spans small-molecule and macromolecular crystallography. Applications include chemistry, materials science, biology, pharmacology, and geology. In biology, macromolecular crystallography reveals the 3D structure of proteins and nucleic acids, informing mechanism and drug design. Data and models are archived in repositories such as the Protein Data Bank (PDB) and the Cambridge Structural Database.

Technological advances—particularly synchrotron radiation, cryogenic data collection, and automated or high-throughput workflows—have increased resolution and throughput. Limitations include the need for well-formed crystals, the phase problem, potential radiation damage, and difficulties in solving structures of flexible or disordered regions.