Comparison between stability, electronic, and structural properties of cagelike and spherical nanodiamond clusters

Ab initio density functional theory calculations were used to investigate cohesive, electronic, and structural properties of cagelike and spherical hydrogen terminated nanoparticles of diamond. Unlike cagelike nanodiamond particles, the variation of calculated energies of spherical ones is not monotonic. The variation range of the calculated energies and bond lengths of cagelike nanoparticles is much tighter than the variation range of spherical ones. In contrast to spherical nanodiamond particles, the C-C bond lengths of all cagelike nanoclusters are very similar to the bond length of bulk diamond. The comparison of stability, electronic highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps, and structural properties of these two classes of nanodiamonds shows that the effects of spatial symmetry, morphology, and C-H atom ratio are more important than the effect of nanoparticle sizes.

Figure 1

Optimized atomic structure of spherical nanodiamond particles. (a) ${\mathrm{C}}_5{\mathrm{H}}_{12}$, (b) ${\mathrm{C}}_{17}{\mathrm{H}}_{36}$, (c) ${\mathrm{C}}_{29}{\mathrm{H}}_{36}$, (d) ${\mathrm{C}}_{35}{\mathrm{H}}_{36}$, and (e) ${\mathrm{C}}_{47}{\mathrm{H}}_{60}$.

Figure 2

(Color online) The variation of formation energy with the size of cagelike and spherical nanodiamond particles.

Figure 3

(Color online) The variation of electronic HOMO-LUMO energy gaps with the size of cagelike and spherical nanodiamond particles.

Figure 4

(Color online) The isocharge surface of (a) HOMO and (b) LUMO states of cagelike nanodiamond particles. The isocharge surface of (c) HOMO and (d) LUMO states of spherical nanodiamond particles.

Figure 5

(Color online) The variation of C-H atom ratio with the size of cagelike and spherical nanodiamond particles.

Figure 6

(Color online) The variation of Mulliken atomic charge with the size of spherical nanodiamond particles.

Figure 7

(Color online) The calculated C-C bond lengths of cagelike nanodiamond particles with different sizes. The solid line shows the C-C bond lengths of diamond lattice.

Figure 8

(Color online) The calculated C-C bond lengths of each spherical nanodiamond particle with different sizes. The solid line shows the C-C bond lengths of diamond lattice.

Figure 9

(Color online) The calculated C-C bond lengths of ${\mathrm{C}}_{47}{\mathrm{H}}_{60}$ spherical nanodiamond particle versus distance from the center of the nanoparticle.