1Helsinki University of Technology, Laboratory of Computational Engineering, PO Box 9203, FIN 02015 HUT, Finland
2TCM Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Ave, Cambridge CB3 0HE, UK
3Imperial College London, Department of Physics, Exhibition Road, London SW17 2AZ, UK
Contrary to previous simulation results on the existence of amorphous intergranular films at high-angle twist grain boundaries (GBs) in elemental solids like silicon, recent experimental results imply structural order in some high-angle boundaries. With a novel protocol for simulating twist GBs, which allows the number of atoms at the boundary to vary, we have found new low-energy ordered structures. We give a detailed exposition of the results for the simplest boundary. The validity of our results is confirmed by first principles calculations.