Multi-scale Non-equilibrium Molecular Dynamics
A Multi-scale
Molecular Dynamics
Algorithm
and Its Simulations
of Dislocation
Propagations
and Simulations of Shock Wave Propagations
Shaofan Li, University of California at Berkeley
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.
T= fixed
T=T+
T=T-
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)
Fig.1 Comparison of E-MD and NEMD
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.
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