Superatom Molecular Orbitals of Li@C₆₀: Effects of the Li Position and the Substrate

Abstract

Understanding the character of superatom molecular orbitals (SAMOs) of fullerenes, especially those of the endohedral fullerenes, can potentially facilitate the utility of these molecules in organic electronics beyond conventional limits. However, the detailed nature of SAMOs in molecular films on substrates has yet to be unraveled. Using density functional theory, we investigate the wavefunction distributions and electronic structures of SAMO states of a Li@C60 monolayer in dependence on the position of Li within the cage and the type of substrate species. We find that the characteristics of the SAMOs in terms of shape and energy are quite sensitive to the Li position due to different charge redistributions. The substrate affects the intermolecular distances in the Li@C60 films and modifies the widths and dispersion of the SAMO bands while retaining energetics similar to that of the isolated Li@C60 monolayer. The substrate also affects the SAMO effective masses, making it possible to tune them via substrate-induced interaction. A properly chosen substrate can so be beneficial for Li confinement and SAMO stability, reflecting the molecule–substrate interaction and the charge transfer at the interface. These findings provide insights into the design and engineering of SAMOs of molecular films.

Superatom Molecular Orbitals of Endohedral C82

“…To understand how endohedral doping affects the SAMO states of the C 82 molecule, we calculated the C 82 cage doped endohedrally by Ca or Sc atoms. Based on previous research, we know that the off-center position inside the cage is the most energetically favorable position for endohedral doping. ,, In the optimized geometry, the Ca and Sc atoms are positioned along the side of the C 82 cage at distances of 2.36 and 2.14 Å, respectively, from the nearest carbon atom, which is close to the previous results for La@C 82 . , The effective position of metal atoms and their distance from the fullerene wall has been previously discussed in various research. , The wave function distributions of different SAMO states, resembling the harmonic shape of s and p orbitals for Ca- and Sc-doped C 82 , are shown in Figure . Comparing the wave function distribution of the SAMO states among C 82 , Ca@C 82 , and Sc@C 82 , the SAMOs for C 82 are symmetric and evenly distributed, whereas for the endohedral-doped C 82 the SAMO states are aligned toward the position of the Ca or Sc atom.…”

“…Overall, it is evident that the endohedral doping of C 82 results in lower energies of the SAMO states as compared to their corresponding empty molecules, while it is also evident that the SAMOs have lower energy in the monolayers than for the stand-alone molecules due to the quantum confinement effect as reported previously . We also noticed from Figure that the wave function distributions of the SAMO states are not majorly altered by altering the lattice parameter of the unit cell, while higher-order SAMO states exhibit significant changes in their energies.…”

“…55,56 The effective position of metal atoms and their distance from the fullerene wall has been previously discussed in various research. 26,57 The wave function distributions of different SAMO states, resembling the harmonic shape of s and p orbitals for Ca-and Sc-doped C 82 , are shown in Figure 2. Comparing the wave function distribution of the SAMO states among C 82 , Ca@C 82 , and Sc@ C 82 , the SAMOs for C 82 are symmetric and evenly distributed, whereas for the endohedral-doped C 82 the SAMO states are aligned toward the position of the Ca or Sc atom.…”

“…It was shown that the location of Li in the upper hemisphere of the fullerene molecule is more stable and that the substrate has a very minor effect on the energy of the SAMO states while greatly affecting the band dispersion and confinement of Li inside the cage. 26 Apart from Li, several articles, both experimental and theoretical, 8,27−33 different metals, clusters, and molecules inside the fullerene cage such as La, Y, Ag, Ca, Sc, He, Ne, and Mn to name a few. Of these encaged metals, several metals exist in +2 and +3 oxidation states.…”

“…The effects of the position of Li inside the cage and of the substrate on the SAMO states in the C 60 fullerene molecule were also studied. It was shown that the location of Li in the upper hemisphere of the fullerene molecule is more stable and that the substrate has a very minor effect on the energy of the SAMO states while greatly affecting the band dispersion and confinement of Li inside the cage …”