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The VH 1 defect in diamond (one hydrogen atom saturating one of the four dangling bonds of the carbon atoms surrounding a vacancy) is investigated at the quantum mechanical level by using the periodic supercell approach, an all electron Gaussian type basis set, “hybrid” functionals and two supercells. Both spin states, characterized by S z = 1/2 and S z = 3/2 and resulting from the unpaired electrons on the three unsaturated carbon atoms around the vacancy, have been investigated. The doublet state VH 1 d turns out to be more stable by 0.34 eV than the quadruplet VH 1 q . The band structure, charge and spin density distributions are analyzed. The two states present very different IR spectra, with peaks that can be used for their characterization. In particular the CH stretching peak can vary by as much as 400 cm −1 : from about 2800 cm −1 for VH 1 q to about 3200 cm −1 for VH 1 d in the harmonic approximation. Anharmonicity is quite important but very different in the two cases: for the C-H stretching, about 330 cm −1 for VH 1 q and only 190 cm −1 for VH 1 d , so that the final anharmonic wavenumbers differ by as much as 500 cm −1 . [ABSTRACT FROM AUTHOR]

The environment dependent interatomic potential (EDIP) including Ziegler–Biersack–Littermark (ZBL) interactions for close encounters is applied to cascades starting from a host atom and from an interstitial atom. We find the room temperature displacement threshold to be 25 eV, increasing to 30 eV at 900 K. The latter correlates well with the measured threshold for vacancy production. Additionally, divacancy production is found to occur, including interlayer divacancies from around 60 eV. The data suggest a new, continuous damage function applies, where the threshold region depends on the square root of the primary knock-on atom (PKA) energy in excess of the threshold, evolving to a linear dependence on PKA energy. [ABSTRACT FROM AUTHOR]