Quantum Crystallography encompasses a huge array of quantum phenomena occurring in crystals. They range from the interaction of crystalline materials with photons of electromagnetic radiation, used to map experimentally the particles (electron) wave functions and densities, to quantum mechanically based materials properties.
This field has witnessed a massive increase of production coupled with a broadening of the scope in the last decade, culminated with the organization of the first Erice School of Crystallography dedicated to this subject (2018).
Originally, the focus was mainly on electron density and derived electrostatic functions (electric potential, field and field gradient). However, a major goal has always been the determination of a wavefunction from experiment, in particular from X-ray diffraction. This would of course enable an exhaustive calculation of all the quantum mechanical functions and properties of the crystal. This has become possible in the last 20 years thanks to the technique devised by Jayatilaka and coworkers (see references below). From this, many methods are derived and currently developed. Often the interest is on the constituents of a crystal, for example molecules in crystals, thus making quantum crystallography a natural partner of computational quantum chemistry.
Methods based on direct determination of the electron density, which were successfully developed in the 1970s, evolved significantly in the past few years leading to the so-called subatomic resolution, using which tiny polarizations of core electrons can be mapped. Moreover, by coupling charge and spin models and using an appropriate mixing of experimental information, the spin resolved electron density can be mapped. Finally, the quantum behavior of materials at extreme conditions is of increasing interest. Far from being routine, all the experimental and computational results of quantum crystallography should be regarded with special attention given the wealth of information on a system that they provide.