Calculation of thermal conductivity of Copper and Nickel metals by molecular dynamics method

Changes of phonon thermal conductivity of copper and nickel crystals with temperature and number of atoms used in the calculation box were investigated by an anisotropic molecular dynamics method. In order to model the interatomic interactions between atoms, Voter-Chen and Mishin versions of EAM were used for nickel and copper, respectively. The equation of motion for the model systems were solved numerically by using Gear predictor-corrector algorithm. The phonon thermal conductivities were determined by utilizing the integration curves for time auto-correlation functions of heat current which calculated from local energy fluctuations. The calculations were repeated for the moleculardynamics cells with 256, 500, 864, 2048, 4000, 6912 and 8788 atoms, and periodic boundary conditions acted on. Each model system were run for 2x105 and 8x105 integration steps in order to get the thermalization and the calculation, respectively. The calculations were carried out at various temperatures in between 0.1-1000 K. Generally, it has been observed that, at the temperatures lower than 10 K, the thermal conductivities change linearly with T, and goes to a maximum value between 8-10 K, and then decrease down to a constant value with T-a. It has not been obtained any remarkable behavior in the thermal conductivity changes depending on the number of atoms, and therefore on the sizeof MD cell. It is conducted that the obtained values of thermal conductivity were generally lower than experimental values, but there are the appropriate qualitative changes with temperature.Key Words: Phonon Thermal Conductivity, Molecular Dynamics, Embedded Atom Method, Fourier?s Law, Heat Current