Development of a Non-equilibrium Molecular Dynamics Simulation Tool for Calculating the Thermal Conductivity of Solid Materials
Date Issued
2007
Date
2007
Author(s)
Chiu, Chun-Ying
DOI
zh-TW
Abstract
A nonequilibrium molecular dynamics method is used to compute the thermal conductivity of bulk silicon and the influence of numerical parameters involved in the method on the computed thermal conductivity k is studied numerically in this thesis. Numerical parameters involved in the method are as follows, M(the number of steps which we take for average), q"(heat flux), δ(the length of the region where heat is added or removed), Lz(the length of the simulation cell in the direction of heat flux), A(the area of the cross section which is perpendicular to the direction of heat flux), and σ(the distance between the region where heat is added or removed and the region we take for linear fitting). By Jund and Julien’s method[19], we rescale the velocity of atoms in heat source and heat sink to add heat flux in the simulation cell. As the simulation cell has reached steady, we can get temperature gradient from a stationary temperature profile and compute the thermal conductivity by Fourier’s law. In the simulation We find the lager q", the longer simulation time is needed for the system to achieve steady state. In general, the bigger σ, the more linear temperature profile and larger k is got. The Larger q", the larger k is got, but the result does not agree with experiments. k is almost not affected by δ and A. Because of the finite-size effect, the Longer Lz, the larger k is got. When q" is too large or δ is too small, we find the stationary temperature profile of the simulation cell is asymmetric. This may be due to the fact that k is smaller at higher temperature. All k's we get in this simulation are smaller than that of bulk Si measured in experiment because the mean free path of phonon is limited by the boundaries at the edge of heat source and sink. Specially, I am grateful to my senior, Tai-Ming Chang for his programs－the subprogram which calculate the force between atoms, the subprogram of Verlet list + Cell link method, the subprogram of computing temperature of slices of the simulation cell, and the method of how to set the initial position of atoms at lattice sites of the periodic boundary condition. Those programs and the method make the research in this thesis completed successfully.
Subjects
熱傳導係數
非平衡分子動力學
尺寸效應
thermal conductivity
nonequilibrium molecular dynamics
finite-size effect
Type
thesis
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