Multi-scale Non-equilibrium Molecular Dynamics and Its Simulations of Dislocation Propagations

1. Multi-scale Non-equilibrium Molecular Dynamicsand Its Simulations of Dislocation Propagations A Multi-scale Molecular Dynamics Algorithm and Simulations of Shock Wave Propagations Shaofan Li, University of California at Berkeley T= fixed The non-equilibrium thermal-mechanical coupling process at small scales is a subject of increasing importance to energy conversion and transfer, cellular and molecular biology, micro- and nano-electronics, and material synthesis and failure analysis. The conventional non-equilibrium MD (NEMD) suffers some major shortcomings for example, when T1=T2=T, NEMD will not spontaneouly return to an EMD (see Fig. 1) Recently, we have developed a multi-scale non-equilibrium molecular dynamics (MS-NEMD) that combines a fine scale local equilibrium MD and a coarse-grained quasi-continuum thermodynamics. T=T+ T=T- Fig.1 Comparison of E-MD and NEMD Fig. 2 Numerical Strategy of MS-NEMD The main technical ingredients of the coarse grain description are: (1) Harmonic approximation, and (2) the Cauchy-Born rule Fig. 3 Concept of Multi-scale canonical ensemble. 1. MD 2. NEMD 3. E-MD 4. MS-NEMD 1. MD 2. NEMD 3. MS-.NEMD Simulations of Shock-wave Propagations: 1. NEMD An external force field, f=0.03 is uniformly distributed in the whole domain. In 1D example, there are 41 elements-cells, and total 1000 MD atoms; and in 2D example, there are 441 FE nodes and 49,401 atoms. 2. MS-.NEMD Fig. 4 Comparisons of MD, EMD, NEMD, and MS-NEMD