Abstract
The vibrational spectra of Ge and Si have been constructed by computation of 174 characteristic frequencies in 29 directions by Born's lattice theory as elaborated by Smith. Two approximations have been considered, involving (a) the interaction between each atom and its first neighbors only, and (b) the interaction between the atom and its first neighbors, and the central force interaction between the atom and its second neighbors. The specific heats of Ge and of Si at low temperatures are calculated from the spectra. The theory indicates a minimum of the Debye characteristic temperature in qualitative agreement with the experiments, but fails to give quantitative agreement.

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