Internal strain in diamond structure elements: a survey of theoretical approaches

The various ways in which the internal strain parameter may be extracted from models of the elasticity and lattice dynamics of diamond structure crystals are surveyed. A general potential having six parameters and involving first and second neighbours gives values that agree with observation in silicon and germanium. The four- or five-parameter adiabatic bond charge model indicates a range of values that embraces the observations. Models that are limited to nearest neighbours and those that extend beyond second neighbours appear generally incapable of predicting reasonable values for the internal strain.