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. 2016 Sep 13;374(2076):20150319.
doi: 10.1098/rsta.2015.0319.

The influence hydrogen atom addition has on charge switching during motion of the metal atom in endohedral Ca@C60H4 isomers

G Raggi  1 , E Besley  1 , A J Stace  2
Affiliations

The influence hydrogen atom addition has on charge switching during motion of the metal atom in endohedral Ca@C60H4 isomers

G Raggi et al. Philos Trans A Math Phys Eng Sci. .

Abstract

Density functional theory has been applied in a study of charge transfer between an endohedral calcium atom and the fullerene cage in Ca@C60H4 and [Ca@C60H4](+) isomers. Previous calculations on Ca@C60 have shown that the motion of calcium within a fullerene is accompanied by large changes in electron density on the carbon cage. Based on this observation, it has been proposed that a tethered endohedral fullerene might form the bases of a nanoswitch. Through the addition of hydrogen atoms to one hemisphere of the cage it is shown that, when compared with Ca@C60, asymmetric and significantly reduced energy barriers can be generated with respect to motion of the calcium atom. It is proposed that hydrogen atom addition to a fullerene might offer a route for creating a bi-stable nanoswitch that can be fine-tuned through the selection of an appropriate isomer and number of atoms attached to the cage of an endohedral fullerene.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

Keywords: calcium; density functional theory; endohedral; fullerene; nanoswitch.

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Figures

Figure 1.
Figure 1.
Six optimized configurations of neutral and ionized Ca@C60H4. Shown at the top of structures (a–f) is a ‘front’ view and underneath is a ‘profile’ view. Structure (f) is the only C60H4 combination known to have been synthesized. (Online version in colour.)
Figure 2.
Figure 2.
Total energy curves calculated for displacement along the x-axis of the calcium atom in neutral Ca@C60H4 in each of the six configurations shown in figure 1. The geometric centre of the fullerene cage is at x=0 and the hydrogen atoms are located on the +x side of the fullerene cage.
Figure 3.
Figure 3.
Same as figure 2, but for [Ca@C60H4]+.
Figure 4.
Figure 4.
Distribution of partial atomic charge for three different positions of the calcium atom (blue cyan) in Ca@C60H4 (isomer a). The carbon atoms are depicted according to the charge they carry: red (negative) and blue (positive), and the hydrogens are the light blue circles. Rather than showing the magnitude of charge, the size of circle is renormalized according to the degree of polarization each atom experiences. Two of the hydrogen atoms overlap with one another.
Figure 5.
Figure 5.
Same as figure 4, but taken from calculations on [Ca@C60H4]+.
Figure 6.
Figure 6.
Charge (in units of e) located on separate hemispheres of the fullerene cage in neutral Ca@C60H4 as a function of the position of the calcium atom on the x-axis. Each of the six configurations in figure 1 is shown separately and results for the right hemisphere include contributions from the four hydrogen atoms.
Figure 7.
Figure 7.
Same as figure 6, but for [Ca@C60H4]+.
Figure 8.
Figure 8.
Charge (in units of e) calculated for calcium atoms in different positions within the fullerene cage, and for the six configurations of neutral and ionized Ca@C60H4 (ionized marked with a ‘+’) given in figure 1.
Figure 9.
Figure 9.
Total energy curves calculated for displacement along the x-axis of the calcium atom in neutral Ca@C60H6 for the configuration shown in the inset. The geometric centre of the fullerene cage is at x=0 and the hydrogen atoms are located on the +x side of the fullerene cage. (Online version in colour.)
Figure 10.
Figure 10.
Same as figure 9, but for Ca@C60H30. (Online version in colour.)
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