EPJ D Topical review - Confining and compressing the atom

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Published on 27 October 2020

A new Review article in EPJD from Jean-Patrick Connerade (Imperial College London and European Academy EASAL Paris) presents a brief introduction to the physics of confined atoms. The subject has acquired importance in the areas of endohedral fullerenes, quantum dots, bubbles in solids (e.g. helium bubbles in the walls of nuclear reactors), atoms trapped in zeolites, impurities in solids, etc. Confining and compressing the atom is considered from the outset as a problem of fundamental atomic physics inherent to basic models such as the Thomas-Fermi and Hartree-Fock approximations to many-electron atoms.

The discussion explores the connection between internal and external compression of the electronic cloud and relates the compressibility of many-electron atoms to the mechanisms underpinning shell filling in the long periods of the Periodic Table, viz: orbital collapse and s-d subshell competition, as well as valence instabilities and fluctuations. Relativistic effects are also considered. Changes induced in the Periodic Table by very high pressures and their effects on chemistry are described. The connection between compressing the electronic cloud in atomic physics and compressing an ideal gas in thermodynamics is discussed and some important differences between them (due to atomic shell structure and to the use of zero temperature models for atomic structure) are pointed out. The subject of confined and compressed atoms is relatively new, with potential applications in many areas. It can be related to chemical pressure in clusters and the physics of reversible ion storage in solids, of interest for Li+ ion batteries used in propulsion. It also has relevance to laser-driven compression experiments. Some directions for further theoretical work are suggested.