Local density functional calculations of the structure and vibratory modes of the substitutional carbon impurity in silicon

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Abstract
The structure and modes of vibration of the substitutional carbon impurity in silicon are determined as follows: firstly the author found the forces between C and Si atoms using a self-consistent LDF calculation of 17-atom clusters CSi4H12. Secondly, he transferred these forces to a larger 99-atom cluster, CSi98 where Si atoms not bonded to the neighbours of the impurity are taken to interact with a Keating potential. This cluster was relaxed and its vibratory modes found. He found the triplet local mode (F2) to lie at 684 cm-1 which is 13% greater than that observed. This mode is very sensitive to the C-Si bond length: a 4% increase in this length leads to a mode frequency within 5% of the experimental result.