Geometric and electronic structures of metal-substituted fullerenes C59M (M5Fe, Co, Ni, and Rh)have been studied using the local spin density formalism. The clusters are found to be stable in the cage structure, while the deformation of the fullerene network due to the substituted metal atom is larger than that due to the substituted boron or nitrogen atom. The electronic structure of C59M varies with the M, and can be described in terms of defect levels in the host fullerene. Deep defect states due to the metal atom appear in the carbon-derived energy gap, and high chemical reactivity is predicted for the clusters. The magnetic moment of the M atom in C59M is found to be almost completely quenched due to the strong hybridization between the orbitals of the M atom and of their neighboring carbons. The vertical ionization potentials and electron affinities are predicted for all the clusters.

Hybrid density-functional calculations are performed to study the structural and electronic properties of Si13 clusters. Three isomers with Cs, C2v, and C3v symmetries are considered. They are and were believed to be the ground state of Si13 in literature. Our studies agree with the most recent local-density-approximation calculation, and show that the Cs isomer has the lowest energy among the three isomers. The vertical ionization potential (VIP) and vertical electron affinity (VEA) are calculated and analyzed for the three isomers. The results suggest that the C2v isomer can be distinguished from the other two isomers experimentally by the VIP measurement, and the C3v isomer by the VEA measurement.

Using first-principles total energy calculations, we found that the doping of Li into (6,0) nanotubes has no insertion barrier if the tube mouth is passivated. The diffusion barrier is extremely small inside the nanotube, and Li atoms prefer to reside along the tube axis. The reaction is strongly exothermic. The Li-Li interaction inside the nanotube is repulsive but strongly screened. These results point to the possibility of realizing a truly one-dimensional atomic wire inside certain small-radius nanotubes that are fabricated inside zeolite channels if Li is used as dopant, but other elements like K would not serve the purpose.

Fe, Cu atoms and CO molecules were manipulated with a scanning tunneling microscope (STM) on a Ag(110) surface, and one or two CO can transfer from the surface and bond with a metal atom through the STM tip [H. J. Lee and W. Ho, Science 286, 1719 (1999); Phys. Rev. B 61, R16347 (2000)]. We perform a density-functional cluster model investigation for the systems. The experimental geometries are validated and understood using the frontier orbital theory. The STM topographic images are reproduced. The vibrational frequencies of the adsorbate systems are obtained by diagonalizing the second-derivative matrices and are in excellent agreement with the experimental measurements. The geometries and C-O stretch frequencies are predicted for systems with the adsorbate metal atom being Co, Ni, Zn, and Ag. These systems can be divided to two classes, and each class exhibits a different set of properties.

We report self-consistent ab initio calculations of structural and electronic properties for the B- and Mgterminated MgB2 (0001) surfaces. We employ ultrasoft pseudopotentials and plane-wave basis sets within the generalized gradient approximation. The surface relaxations are found to be small. The surface prefers to be terminated by Mg atoms. For the B-terminated surface, both B s and p surface bands appear, while only one B p surface band exists near the Fermi level for the Mg-terminated surface. The work function is predicted to be 5.95 and 4.25 eV for the B- and Mg-terminated surfaces, respectively. The simulated scanning tunneling microscopy images of the surfaces are not sensitive to the sign and value of the bias voltages, but depend strongly on the tip-sample distance. An image reversal is predicted for the Mg-terminated surface.