ENERGY-MINIMIZATION STUDIES OF TWIST GRAIN-BOUNDARIES IN DIAMOND

We study the zero-temperature energy and atomic structure of twist gra in boundaries (GB's) in diamond, using a semiempirical potential due t o Tersoff. The (111) twist GB energies are similar to predictions of a n empirical tight-binding potential. For the previously unstudied (001 ) twist boundaries in diamond, both the energy and the excess volume a re insensitive to misorientation at large twist angles, although small energy cusps exist for the so-called SIGMA5 GBs. The (001) twist GB e nergies are typically almost-equal-to 6 J/m2. Significant atomic relax ation occurs only in the two atomic layers nearest the grain boundary. Atoms in these contact layers are predominantly threefold coordinated . For (001) twist GB's, in-plane translations significantly affect the SIGMA5(001) energies, but not the SIGMA(n) energies, with n large.