Anharmonicity of the hydrogen-carbon stretch mode on diamond (111)-1×1

The structural and vibrational properties of the hydrogen-capped diamond (111)-1\ifmmode\times\else\texttimes\fi{}1 surface are calculated using a first-principles total-energy approach. The stretching vibration of the hydrogen-carbon bond on the surface and, in particular, its anharmonicity are investigated. The calculated stretch-mode frequency is in agreement with experimental results from sum-frequency generation measurements to within 2.5%. The frequency shift arising from the anharmonicity, i.e., the difference between the overtone frequency and twice the fundamental frequency, is predicted to be 0.014 eV or 113 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. This rather large anharmonicity should make it possible to measure directly the overtone frequency by near-infrared absorption.