Structural relaxation and relative stability of nanodiamond morphologies

Presented here are the results of ab initio Density Functional Theory (DFT) relaxations performed on nanocrystalline diamond structures of cubic {100}, octahedral {111} and cuboctahedral morphologies, up to approximately 1 nm in diameter. Results show that in this size range, the crystal morphology plays an important role in the structural stability of the crystals, in the absence of external fields. While the surfaces of the cubic crystals exhibited reconstruction and relaxations comparable to that of bulk diamond, the surfaces of the octahedral and cuboctahedral crystals showed the transition from sp³ to sp² bonding. Our results demonstrate the inward transition of nanodiamond clusters into carbon onion-like structures, with preferential exfoliation of the (111) surfaces, in agreement with recent experimental observations. The results of this study will provide a better understanding of the effects of nanodiamond morphology on the stability of diamondoid nanostructures and nanodevices.