Ab initio modelling of the stability of nanocrystalline diamond morphologies

Ab initio (density functional theory) relaxation of nanocrystalline diamond structures of cubic, octahedral and cuboctahedral morphologies, up to about l.3 nm in diameter are presented. Results show that the crystal morphology plays an important role in the structural stability, in the absence of external fields. Our results illustrate the transition of nanocrystalline diamonds (nanodiamonds) into onion-like structures showing preferential exfoliation of the (111) surfaces, in agreement with experimental observations. The cohesive energy for the relaxed nanodiamond is also examined and compared with bulk diamond. We have found that the cohesive energy of nanodiamond differs from that of bulk diamond by approximately 0.34 eV.