What is Quantum Crystallography?

Piero Macchi

Politecnico di Milano

e-mail: piero.macchi@polimi.it

The interplay between the two disciplines is quite historical [1,2,3], although often not recognized because the applications of crystallography span a broad range of fields. Crystallography deals with the study of the structure and behavior of crystals. Crystals could be themselves quantum objects (quantum crystals, quantum magnets, quantum materials, etc.) but could play also the role of an intermediate lens which enables the visualization of quantum mechanical functions and properties of the material. This was one of the original goals of the work of Bragg, although not the most well known one. He in fact was the first to propose, by means of diffraction experiments on crystals, the atomic radial density distribution, years before a quantum mechanical wavefunction was obtained theoretically.

The purpose of this introductory talk is to find answers to the title, by provoking the audience and the speakers with some fundamental questions: what is the inner connection between crystals and quantum mechanics? what is a quantum crystal? why “electrons and photons” (the title of the famous Solvay conference 1927) is read by us mainly as “X-ray diffraction”?

References:

[1] Macchi P. Quantum Crystallography: Expectations vs. Reality. Spring Briefs in Crystallography, Springer, 2022;

[2] Macchi, P. The connubium between crystallography and quantum mechanics. Cryst. Rev., 2020, 26, 209-268;

[3] Genoni, A.; Macchi P. Quantum Crystallography in the Last Decade: Developments and Outlooks. Crystals, 2020, 10, 476