Pradeep Pratapa presents “On Predicting Defect Nucleation in Atomistic Simulations” as part of the Data & Materials Chalk & Talk Seminar Series.

Abstract

The talk will be focused on methods for predicting the nucleation of defects in atomistic simulations. The prediction of instabilities in the context of atomistic and homogenized atomistic systems shall be discussed. First, we develop an iterative, linear-scaling framework based on the Lanczos algorithm for determining the onset and mode of instability in atomistic systems. We utilize the proposed formulation to demonstrate that during nanoindentation induced dislocation nucleation, the trajectories of atoms through configurational space are significantly more complicated than those associated with pure slip. Further, through an example of hydrostatically triggered cavitation, we establish that localizing the stability analysis and employing cutoffs for the interatomic potential can both lead to spurious instabilities. Next, based on the Legendre-Hadamard condition, we develop a variant of the conjugate gradient method for predicting defect nucleation in homogenized atomistic systems. We utilize the proposed approach to determine the ideal strength of Aluminum when subject to uniaxial and hydrostatic stresses. In particular, we demonstrate that defects do not nucleate even in the presence of extremely large compressive hydrostatic stresses. Additionally, we show that smaller stresses are required for homogeneous dislocation nucleation in uniaxial compression compared to uniaxial and  hydrostatic tension.

Bio

Pradeep is a second year PhD student in the department of Civil & Environmental engineering at Georgia Tech, specializing in the area of Mechanics & Materials. He is advised by Prof. Phanish Suryanarayana and is currently working on developing a linear scaling code for electronic structure calculations using Kohn-Sham Density Functional Theory. The work aims to develop the code for massively parallel architectures in order to study large systems of atoms at extreme conditions. Pradeep got his Bachelor's degree from Indian Institute of Technology Madras and has a Masters from The University of Texas at Austin.