AbstractThe application of the Coincidence site lattice (CSL) model to the diamond cubic structure allows a purely geometric modelling of specific grain boundaries. Symmetric ⟨011⟩ CSL tilt boundaries with [Sgrave] ≤ 33 were constructed with energies lower than the energy of a random boundary. Structures without broken bonds were found for rotation angles θ ≤ 70·53°. Boundaries within the range θ ≤ 26·53° ([Sgrave] = 19) are considered as small-angle boundaries consisting of an array of edge dislocations.