Transition saddle points and associated defects for a triaxially stretched FCC crystal

Abstract

We demonstrate the use of a single-ended method for locating saddle points on the potential energy surface for a triaxially stretched FCC crystal governed by a Lennard-Jones potential. Single-ended methods require no prior knowledge of the defected state and are shown to have powerful advantages in this application, principally because the nature of the associated defects can be quite complicated and hence extremely difficult to predict ab initio. We find that while classical spherical cavitation occurs for high stretch values, for lower values the defect mode transitions to a non-spherical pattern without any apparent symmetries. This non-spherical mode plays the primary role in harmonic transition state theory predictions that are used to examine how instabilities vary with applied loading rate. Such a defect mode would be difficult to determine using double-ended methods for finding saddle points.