Tight-binding study of tilt grain boundaries in diamond

We have examined a number of symmetric tilt grain boundary structures in diamond, using a transferable tight-binding (TB) carbon potential. Utilizing O(N) tight-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 \ensuremath{\Sigma}=3 70.53\ifmmode^\circ\else\textdegree\fi{} grain boundary. For angles less than 70.53\ifmmode^\circ\else\textdegree\fi{}, the boundaries are composed of a series of b=〈011\ifmmode\bar\else\textasciimacron\fi{}〉 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. \textcopyright{} 1996 The American Physical Society.