Atomic compressibility and reversible insertion of atoms into solids

Abstract

We developed a theoretical model to investigate the compressibility of atoms. Atoms are confined inside a spherical cavity, simulated numerically by a finite repulsive potential barrier. The energy levels and wavefunctions of confined atoms are determined by solving, for different cavity radii, the relativistic Dirac-Fock equations, including formally the repulsive barrier. The changes in the atomic size and in the ground-state energy level allow one to define a positive isotropic pressure exerted on the confined atom. The model is applied to atomic caesium and it is demonstrated quantitatively that the remarkable compressibility of caesium originates from a purely atomic mechanism, namely the pressure-induced collapse of the 5d orbital. We propose that this mechanism can also drive, at an atomic level, a reversible insertion of atoms into solids. Applications to lithium-ion batteries are briefly discussed at the end of this paper.

Structure and photoionization of confined atoms

“…The calculations reviewed in this section give only a first insight into the rather complex problem of confined quantum systems. Effects which remain to be better understood to complete the theory to its logical end are the LS dependence of orbital collapse for some critical cases, the influence of multiplet structure on level crossings, as well as the manner in which relativistic effects should be built into the theory (Connerade and Semaoune, 2000a), so that heavier species can be included. Once all this is achieved, the whole periodic table will be established within a single consistent theory for confined atoms.…”

“…Consistent study of the modifications of outer wavefunctions in multielectron atoms and the ability of these atoms to rearrange their structure upon being compressed was recently detailed by and Connerade and Semaoune (2000a). In this subsection, we give examples that atoms exhibiting orbital collapse, i.e., essentially all the transition atoms with regard to d-and f-orbital collapse are extremely sensitive to an increase in the pressure on the atom.…”

“…Also, demonstrated was the effect of ''autoionization'' of atoms by pressure, similar to that discussed by Sommerfeld and Welker (1938) and by Varshni (1998) for ionization of hydrogen by pressure, although, of course, for a multielectron atom, there is a richer variety of phenomena, owing to the presence of more than one ionization threshold. Finally, Connerade and Semaoune (2000a) extended non-relativistic calculations of multielectron atoms confined in an impenetrable spherical box model to relativistic Dirac-Fock calculations, to detail pressure induced modifications in heavier atoms of d-series where they found dramatic importance of relativistic effects, in some cases. The application of this relativistic model to atomic caesium showed that the remarkable compressibility of caesium originates from a purely atomic mechanism, namely the pressure induced orbital collapse of the 5d orbital of Cs.…”

“…However, for heavy elements, a full treatment of relativistic effects would really be necessary. The problem of confined atoms with inclusion of relativistic effects was modelled by Connerade and Semaoune (2000a). The applicability of the model was tested by comparing the calculated and experimental data (Takemura et al, 1981) for atomic size of the Cs atom versus pressure.…”

“…o and Mih! aly, 2001), the chemical reactivity and chemical valence of atoms (Lawrence et al, 1981), the reversible storage of ions in certain solids (Connerade, 1997;Connerade and Semaoune, 2000a), the appearance of helium bubbles under high pressure in the walls of nuclear reactors (Walsh et al, 2000), and ESR, NMR and magnetic moments of compressed atoms (Buchachenko, 2001), etc. Confined atoms are also very close in principle to the concepts underpinning confinement within ''quantum dots'' (Johnson, 1995;Sako and Diercksen, 2003a, b).…”