Efficiency and fidelity of molecular simulations relevant to dislocation evolutions

The comparative simulations of dislocation evolution in nanoindentation are carried out in terms of both molecular dynamics (MD) and energy minimization (EM) methods, to explore what really govern the computational efficiency and fidelity in molecular simulations relevant to dislocation evolutions. It is found that although all simulations can present similar relationship between indentation force and depth, there still might be some significant differences in the simulated dislocation patterns and computational efficiency. Firstly, the EM simulations show more complicated dislocations. Secondly, the necessary computational effort of EM increases nonlinearly with indentation depth, compared to the linear dependence in MD simulations, namely EM shows higher efficiency than MD in shallow indentation, but vice versa in deeper ones. More importantly, it is revealed that the time consumption of the minimization iteration is strongly dependent on the moving of dislocation loops and increases greatly when dislocation loops move long distances. Whereas MD simulations of complicated dislocations patterns may need less time cost but present immature dislocation evolutions, since the relaxation steps in MD simulations are fixed beforehand, regardless of the dislocation loops moving to equilibrium state or not. (C) 2017 Elsevier B.V. All rights reserved.