A General Valence Force Field for Diamond

Expressions are obtained which relate the force constants of a general valence force field to the macroscopic elastic constants and the Raman frequency of diamond-type crystals. When values of the valence force constants derived from the frequencies of the neopentane molecule are used in these expressions, poor agreement is found with the observed physical constants of diamond. It is suggested that the interaction constant associating bond extension with angular deformation is most seriously altered in the diamond structure, but a more definite conclusion must await improved experimental determinations of the elastic constants.