Quantum Crystallography: N-Representability Big and Small**

Linus Pauling contributions span structural biology, chemistry in its broadest definition, quantum mechanical theory, valence bond theory, and even nuclear physics. A principal tool developed and used by Pauling is X-ray (and electron) diffraction. One possible extension of Pauling's oeuvre could be the marriage of crystallography and quantum mechanics. Such an effort dates back to the sixties and has now flourished into an entire subfield termed Quantum Crystallography. Quantum Crystallography could be achieved through the application of Clinton equations to yield N-representable density matrices consistent with experimental data. The implementation of the Clinton equations is qualitatively different for small and for large systems. For a small system, quantum mechanics is extracted from X-ray data while for a large system, the quantum mechanics is injected into the system. In both cases, N-representability is imposed by the use of the Clinton equations.

Automated summary

Linus Pauling made significant contributions to various scientific fields, including structural biology, chemistry, and quantum mechanics. He developed and used X-ray and electron diffraction as principal tools in his work. His research laid the foundation for the development of Quantum Crystallography, which combines crystallography and quantum mechanics.