DFT Calculations of Vibrational Spectra of Oxidized (111) Diamond Surface

First principle calculations based on the density functional theory were used for calculating the vibrational modes of the C=O bond on the (111) surface of oxidized diamond nanoparticles. From preliminary considerations, the carboxylic and anhydride groups were the most contributing to the spectral bands observed in the experimental FTIR spectra in the range of 1600–1950 cm^–1. Small clusters of the ideal H-terminated (111) surface layer occupied by 1–4 carboxylic or anhydride groups were studied computationally. Compared to the available spectra databases of the carboxylic acids, the calculated C=O peak position of the isolated surface-bonded carboxyl is shifted to higher frequencies. On the other hand, the isolated anhydride connected to the diamond surface by both its ends does not show a significant shift. The mutual influence of neighboring functional groups vibrations due to the dynamic dipole effect was identified. The analysis helped to understand the changes which the nanoparticles underwent during the oxidation.