First principles quantum molecular dynamics applied to silicon surface reconstructions, fullerenes, and novel carbon solids

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:7138707

Adams, G B

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].

• Research Organization: Arizona State Univ., Tempe, AZ (United States)
• OSTI ID: 7138707
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
CARBON COMPOUNDS
DYNAMICS
MOLECULAR STRUCTURE
FULLERENES
SILICON
CHEMICAL BONDS
MOLECULAR MODELS
QUANTUM MECHANICS
SURFACES
CARBON
ELEMENTS
MATHEMATICAL MODELS
MECHANICS
NONMETALS
SEMIMETALS
665400* - Quantum Physics Aspects of Condensed Matter- (1992-)
360602 - Other Materials- Structure & Phase Studies