A stable hollow AuSi cage with I symmetry has been predicted using first-principles density functional theory. The stability of the cage-like AuSi structure is verified by vibrational frequency analysis and molecular dynamics simulations. A relatively large highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.057 eV is found. Electronic structure analysis shows that clearly p-d hybridizations between Si atoms and Au atoms are of great importance for the stability of AuSi cage. The cage-like AuSi structure may have potential applications in semiconductor industry and microelectronics.

A stable hollow copper silicide cage with Ih symmetry, Cu20Si12, constituted of a copper dodecahedron and a silicon icosahedron, was investigated using density functional theory. Molecular dynamics simulations show that Cu20Si12 retains its geometric topology up to an effective temperature of about 962 K. The molecule has a HOMO-LUMO gap of 1.099 eV, indicating its relatively high chemical stability. These frontier molecular orbitals show clear characteristics of hybridization between Si 3p and Cu 3d electrons. This proposed structure helps to extend the range of high-symmetry molecular polyhedral species. The hollow space within Cu20Si12 can be used to accommodate other atoms or molecules and emphasizes the benefit of studying endohedral fullerenes.

Ling-Yan( ) a) , Shi Yan-Li( ) b) , and Zhang Zhi-Ming( ) b) †

A stable core–shell Mg20B24 structure has been constructed and investigated using first-principles calculations. This molecule consists of a boron icosahedron core with an Ih symmetry and a pentakis dodecahedron shell composed of an intercalated boron icosahedron and magnesium dodecahedron. Frequency analysis shows that the molecule was static stable, and its highest frequency of 685.4 cm–1 corresponds to the powerful “breathing” mode of the B12 core, and the lowest frequency is 141.6 cm–1 due to the vibrations of the outer shell. The molecular dynamics calculations suggest that it is stable at about 1600 K. Results show that the molecule has a highest-occupied molecular orbital–lowest-unoccupied molecular orbital gap of about 1.07 eV. This molecule may be a promising hydrogen storage material. There presents a double-shell distribution of absorbed H2 molecules for this molecule, and ∼175 H2 molecules are adsorbed on Mg20B24, with the gravimetric hydrogen density reaching ∼32.1%.

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