Tight-binding study of tilt grain boundaries in diamond

We have examined a number of symmetric lilt grain boundary structures in diamond, using a transferable tight-binding (TB) carbon potential. Utilizing O(N) light-binding molecular dynamics, we are able to simulate several thousands of atoms, allowing us to examine low-angle boundaries with large periodicities. The lowest energy structure is the {111} twin boundary, corresponding to the Sigma = 3 70.53 degrees grain boundary. For angles less than 70.53 degrees, the boundaries are composed of a series of b = [01(1) over bar] edge dislocations. The core structures of : these dislocations are composed of five- and seven-atom rings. For these low-angle structures, the tight-binding energies have trends similar to those found using a Tersoff potential; both models give results that are consistent with linear elasticity theory. For the high-angle {211} and {311} boundaries, the tight-binding model predicts a reconstruction along the [011] direction, in order to eliminate dangling bonds.