A Multi-Scale Method for Non-Linear Mechanical Behavior of Nanostructures Based on Coarse-Grained Model

Vokhshoori Koohi, Melika | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 51550 (53)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Khoei, Amir Reza; Jahanshahi, Mohsen
  7. Abstract:
  8. The ever-increasing growth of Nanotechnology has elevated the necessity for the development of new numerical and computational methods that are better capable of evaluating systems at this scale. The existing techniques, such as Molecular Dynamics Methods, in spite of being fully capable of evaluating nanostructures, lack the ability to simulate large systems of practical size and time scales. Therefore, in order to be able to provide a realistic simulation of a large model, simulation of which is limited by the computational cost of the current molecular dynamics methods at hand, Coarse-Graining technique has recently become a very effective and beneficial method which refers to the development of simplified models of molecular systems with reduced number of degrees of freedom which is achieved by reducing the number of interaction sites, resulting in a model that is computationally less expensive than the original atomistic model. Up until recently, the coarse-grained models have only been used to simulate large biomolecules such as proteins, lipids, DNA, and polymers since they consist of massive and complex structures which make them impossible to be modeled by previous molecular methods available. However, in this research, we have focused on applying the Iterative Boltzmann Inversion Coarse-Graining Technique to FCC metal crystal structures in order to be able to simulate larger models of practical size, modeling of which would be time and energy consuming by the molecular dynamics methods available. In this particular technique, the goal is to determine a Coarse-Grained potential in such a way that the target radial distribution function of the reference all-atom system, which structurally characterizes the atomistic system, is reproduced. At the beginning of this research, no actual coarse-graining was performed and the aim was to simply develop an interatomic potential for the all-atom system using the Iterative Boltzmann Inversion method and investigate the efficiency of this newly developed potential in representing the all-atom model simulated using VII the EAM potential. Due to a few drawbacks of the IBI method such as failing to produce state-independent potentials, we also investigated the influence of the Multi-State Iterative Boltzmann Inversion Technique on reducing state dependency. In general, the aim of Multi-State IBI, as an extension to the standard IBI method, is to derive a potential that can be used over various thermodynamic states. Once the effectiveness of the IBI method in producing a pair-wise potential to simulate an all-atom model was adequately studied, coarse-graining was conducted and the mechanical behavior of the all-atom system was compared to that obtained from a coarse-grained system, the potential of which was developed using the IBI method. At the end, the efficiency of this developed potential in simulating larger models was studied
  9. Keywords:
  10. Nonlinear Behavior ; Molecular Dynamic Simulation ; Multiscale Modeling ; Mechanical Behavior ; Coarse Grain Molecular Dynamic

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