The connubium between crystallography and quantum mechanics

Abstract

By rephrasing the incipit of one of the most influential books: a spectre is haunting science, the spectre of quantum crystallography. This name is ever more frequent in the scientific literature and very appealing. Though, what does it reflect? Both crystallography and quantum mechanics are branches of science, although perceived in an inappropriate way: crystallography is often a synonymous for X-ray diffraction whereas quantum mechanics is intended as computational physics or chemistry. Both diffraction and computation are not sciences, but techniques. Establishing the quantum mechanical paradigm was one of the most important scientific revolutions, which changed the perspective of physics and unveiled the nature of small particles. Instead, crystallography is an old science, anciently started when the search for naturally grown materials was vital. The curiosity for crystal morphologies and growth led to more in-depth descriptive analyses and classifications of minerals. Contemporarily, the mathematical description of periodic structures developed. Everything changed abruptly when X-rays were discovered, offering a new light to look inside crystals and unveil their content at an atomic resolution, and even beyond, where quantum mechanics dominates. The purpose of this review is to illustrate how profound and long standing is the entanglement between the two sciences.