Stiffness-Based Coarse-Grained Molecular Dynamics

Abstract

This paper presents a novel technique for the simulation of a nano/micro-material system known as stiffness-based coarse-grained molecular dynamics (SB-CG-MD), which aims to extend the arena of conventional all-atom molecular dynamics (AA-MD) to a greater length and time scale while still capturing atomistic effects. The solution region is modeled on a mesh, and its governing equation is derived solely (yet rigorously) from that of AA-MD through a kinematic constraint and Taylor series expansion. The governing equation of SB-CG-MD resembles that of classical finite element analysis; however, the stiffness matrix is constructed from the interatomic potential instead of stress-strain relation. As a result, the degrees of freedom (DOF) of the simulated material system are reduced from the number of atoms involved to the number of nodes of all elements in the finite element mesh. When the element size shrinks to the atomistic scale, the mesh nodes coincide with atomic sites. To test the capability and sensitivity of SB-CG-MD, the dynamic responses of a series of magnesium oxide bars under mechanical excitation are studied systematically. The results show that the size of an element can be set as large as hundreds of atoms; the accuracies of wave speed and peak value are still kept within an acceptable range (10%), but the computational efforts are reduced dramatically.