New theory provides answers to why metals have the structures that they do

Amazing stuff! We don't even understand elemental metals that well in the 21st century!

"A simple, new theory that can explain why a metal forms a particular structure has been developed. The method allows researchers to understand and predict structures in solid compounds and alloys over a wide range of conditions. ‘This theory is based on our finding that the electrons in many metals occupy so-called quasi-atom orbitals, which are local quantum orbitals centred at the voids between atoms,’ ... ‘The chemical interactions between such localised electrons control the metal structures,’ ..."

From the significance and abstract:

"Significance

The driving force determining the structures of simple metals has been a matter of debate for over a century and has become more puzzling with the discovery of highly complex structures that emerge at high pressures in these materials. Conventional free-electron-based theories fail to provide a unified and predictive mechanism due to missing key components, i.e., local bonding and orbital interactions. These missing components can be represented by quasi-atoms and corresponding local orbitals, a consideration of which can explain the stability of both simple and complex different structures of elemental metals over a wide range of conditions. The results have implications for the behavior of more chemically complex materials, including alloys, intermetallics, hydrides, ionic compounds, and two-dimensional materials.

Abstract

Most metals adopt simple structures such as body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP) structures in specific groupings across the periodic table, and many undergo transitions to surprisingly complex structures on compression, not expected from conventional free-electron-based theories of metals. First-principles calculations have been able to reproduce many observed structures and transitions, but a unified, predictive theory that underlies this behavior is not yet in hand. Discovered by analyzing the electronic properties of metals in various lattices over a broad range of sizes and geometries, a remarkably simple theory shows that the stability of metal structures is governed by electrons occupying local interstitial orbitals and their strong chemical interactions. The theory provides a basis for understanding and predicting structures in solid compounds and alloys over a broad range of conditions."

New theory provides answers to why metals have the structures that they do | Research | Chemistry World The simple concept shows that a metal’s structure results from chemical interactions between localised electrons, challenging the traditional free electron gas model

Chemical interactions that govern the structures of metals (no public access, but Google Scholar provides this link to the full article)

Fig 1 Electron localization and sublattice interactions in metals