Infrared spectra of hydrogenated nanodiamonds by first-principles simulations

The heat of formation and infrared spectra of hydrogenated nanodiamonds with different morphologies (up to 1.92 nm in diameter) have been investigated using density functional theory. Preferential growth orientation along 〈1 1 1〉 orientations corresponding to an octahedral shape was observed according to the computed heat of formation. The simulated infrared (IR) spectra show distinct dependence on both size and morphology of the nanodiamonds. The major IR peaks in the region of 900–1300 cm−1 shift toward high wavenumber as the nanocluster size increases, while the C–H vibrations in the range 2500–3500 cm−1 show an opposite trend. The present results would be useful for identifying the size and morphology of nanodiamonds in experimental IR spectroscopy.