Geometric and electronic properties of endohedral Si@C74.

The generalized gradient approximation based on density functional theory is used to analyze the geometric and electronic properties of Si@C74. It is found that among the five possible optimized geometries of Si@C74, the most favorable endohedral site of Si atom is under the center of a pentagon ring on the σh plane, i.e., Si@C74-5, which is different from the center stable site for Si in C74 calculated by the semiempirical molecular orbital calculations and molecular mechanics calculations, and it is also different from the stable site, i.e., under a [6, 6] bond along the C2 axis on the σh plane in C74 for metal atoms Ba, Ca, and Eu. The deformation charge density on the σh plane reveals that the Si–C bonds in Si@C74-5 have covalent character, while the Mulliken charge analysis together with a longer Si–C bond length reveals that the Si–C bonds in Si@C74-5 have ionic character. Therefore, we infer that Si–C bonds in Si@C74-5 contain both covalent and ionic characters. [ABSTRACT FROM AUTHOR]