Molecular Dynamics
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Molecular Dynamics Fengzhou Fang* and Pengzhe Zhu State Key Laboratory of Precision Measuring Technology & Instruments, Centre of MicroNano Manufacturing Technology, Tianjin University, Tianjin, China
Synonyms Atomistic modeling; Atomistic simulation; MD; Molecular dynamics simulation
Definition Molecular dynamics (MD) method is a computer simulation technique by which the atomic trajectories of a system of N particles are generated by numerical integration of Newton’s equation of motion, for specific interatomic potentials, with certain initial conditions and boundary conditions. MD can provide atomistic details of a wide range of processes and systems. Here MD is employed to study the material removal mechanism in nanometric cutting process.
Theory and Application Introduction
Since the first paper reporting MD simulation was published (Alder and Wainright 1957), MD has been widely employed in a number of scientific fields such as physics, chemistry, biology, and materials science. Research on MD simulations of cutting started in the early 1990s and has attracted more and more attention recently.
Theory
There are five main ingredients to a MD simulation, which are boundary condition, initial condition, interaction potential, integrator, and property calculation. Boundary Condition Generally, there are two major types of boundary conditions: isolated boundary condition (IBC) and periodic boundary condition (PBC). In IBC, the system is presumed to be surrounded by vacuum and the particles just interact among themselves. In PBC, the N-particle cell is surrounded by infinitely replicated, periodic images of itself. Therefore a particle may interact not only with particles in the same cell but also with particles in adjacent image cells. It should also be noted that in a system mixed boundary conditions can be adopted. That is to say, the system is assumed to be periodic in some directions but not in the others.
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CIRP Encyclopedia of Production Engineering DOI 10.1007/978-3-642-35950-7_16729-1 # CIRP 2014
Initial Condition The initial condition means the initial particle positions and velocities of the modeling system. It is easy to generate initial conditions for crystalline solids, but it would take some work for liquids and amorphous solids. A common strategy to create a liquid configuration is to melt a crystalline solid. The amorphous solid configuration is usually obtained through a melting and quenching simulation. Interaction Potential The motions of particles obey the Newton’s equations of motion: mi
d 2 ri! ! @U ¼ F @ r! dt 2
i ¼ 1, 2, . . . , N
(1)
i
The forces are usually derived as the gradient of a potential energy function U which depends on the positions of the particles. Therefore the potential energy function determines the dynamics of particles in the system. In some cases, MD simulations are designed to predict the behavior of generic atoms or particles. Thus, simple (two-body) pair potentials such as Lennard–Jones (LJ) potent
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