부산대학교 도서관

A local-orbital-based first principles quantum molecular dynamics (QMD) method was applied to silicon surface reconstructions, fullerene molecules, and novel carbon solids. The Si(111)-(2x1) buckled chain model was obtained from the Si(111) bulk terminated surface by QMD relaxation. Similarly, the Si(100)-(2x1) asymmetric dimer model and the Si(100)-p(2x2) and -c(4x2) reconstructions were obtained by QMD relaxation from the Si(100) bulk terminated surface. For the Si(111)-(5x5) reconstruction, a Jahn-Teller distortion, occurring at low temperature, was discovered. This Jahn-Teller distortion was revealed by QMD relaxation and verified by the use of perturbation theory. Aluminum deposited on Si(100) was found to dimerize in a direction parallel to, rather than perpendicular to the underlying silicon dimers. The QMD method was applied to 54 different fullerene molecules, from C[sub 20] to C[sub 240]. For the lowest energy forms of the fullerenes C[sub 60], C[sub 70], and C[sub 84], the method was used to determine bondlengths, electronic eigenvalues, and vibrational modes and frequencies. For C[sub 60] the calculated bondlength are within 0.5% of experiment, and calculated vibrational frequencies are from 4% to 16% different from experiment. A single Stone-Wales transformation was found to raise the energy of I[sub h] C[sub 60] by 1.68 eV and the energy barrier for this transformation, measured from the energy of I[sub h] C[sub 60], was found to be 8.4 eV. For the larger ball-like and capsular fullerenes, and for graphitic tubes, empirical equations were developed which reproduce the QMD energies of these structures to better than 4%. These equations are based on a single parameter, the planarity of the molecules. Finally, the QMD method was applied to three novel carbon solids. The lowest energy of the three is a tiling of the D periodic minimal surface with 24 atoms per unit cell and has an energy/atom compared to graphite which is half that of C[sub 60].