Multi-paradigm multi-scale modeling of dynamical crack propagation in silicon using the ReaxFF reactive force field
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0904-BB04-28.1
Multi-paradigm multi-scale modeling of dynamical crack propagation in silicon using the ReaxFF reactive force field Markus J. Buehler1, Adri C.T. van Duin2, William A. Goddard III2 1
Massachusetts Institute of Technology, Cambridge, MA 02139, USA Materials and Process Simulation Center, California Institute of Technology, Pasadena, 91125, CA 2
ABSTRACT We report a study of dynamic cracking in a silicon single crystal in which the ReaxFF reactive force field is used for ~3,000 atoms near the crack tip while the other 100,000 atoms of the model system are described with a simple nonreactive force field. The ReaxFF is completely derived from quantum mechanical calculations of simple silicon systems without any empirical parameters. Our results reproduce experimental observations of fracture in silicon including details of crack dynamics for loading in the [110] orientations, such as dynamical instabilities with increasing crack velocity. We also observe formation of secondary microcracks ahead of the moving mother crack. We conclude with a study of Si(bulk)-O2 systems, showing that Si becomes more brittle in oxygen environments, as known from experiment. Figure 1: The interpolation method for defining a mixed Hamiltonian in the transition region between two different paradigms, as implemented in the CMDF framework. As an alternative to the linear interpolation, we have also implemented smooth interpolation function based on a sinusoidal function. This enables using slightly smaller handshake regions thus increasing the computational efficiency.
INTRODUCTION Brittle fracture is characterized by breaking of atomic bonds leading to formation of two new materials surfaces. Most existing atomistic models of fracture assume an empirical relationship between bond stretch and force. However, breaking of bonds in real materials is an extremely complicated process that could previously only be captured with sufficient accuracy only by using quantum mechanical (QM) methods, which are limited to ~100 atoms. Here we present a new theoretical concept based on building a multi-scale simulation model completely derived from QM principles, while being computationally efficient and capable of treating thousands of atoms with QM accuracy. Fracture of silicon has received tremendous attention due to its complexity of bond breaking and due to interesting failure dynamics observed experimentally [1-5]. These experimental efforts led to critical insight into deformation modes, such as the mirror-mist-hackle transition and orientational dependence of crack dynamics in silicon single crystals [2]. Atomistic modeling fracture of silicon has been the subject of several studies using empirical force fields [5-9]. In contrast to many metals, where fracture and deformation can be described reasonably well using embedded atom (EAM) potentials [10-12], a proper description of fracture in silicon has proved to be far more difficult, requiring a more accurate treatment of the atomic
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