LOCAL ANALYSIS OF STRUCTURAL INSTABILITY IN STRESSED LATTICES - CRACKNUCLEATION IN A COVALENT SOLID

For the local analysis of structural instability, a site-dependent mea sure of local contribution to a global mode is introduced which is dec omposed into contributions from individual interatomic bonds. Since th is measure incorporates both spatial and dynamical information, the me thod provides insight into the temporal evolution of the lattice insta bility. Using this method to study lattice decohesion under pure dilat ion, we find the crack nucleation process to consist of the onset of i nstabilities at several distinct sites, followed by coalescence of loc al instabilities which triggers the bond rupturing along a plane.