Molecular Dynamics Study on the Anisotropic Thermal Conductivity of Helium–Xenon Binary Nanocrystal Superlattices

摘要

The anisotropic thermal conductivity of helium–xenon binary nanocrystal superlattices (BNSLs), which are stoichiometric solid structures Xe(He)₂ and Xe(He)₁₃, at high pressure and room temperature (T = 300 K), respectively, has been calculated by equilibrium molecular dynamics (EMD) simulation using the Green–Kubo formalism and the exponential-6 intermolecular potential under periodic boundary conditions (PBC). The pressures obtained from EMD agree very well with those from an independent study, to within 5 %. Nonequilibrium molecular dynamics (NEMD) simulation is also carried out for comparison. The thermal conductivities predicted by NEMD are of the same order of magnitude as the results predicted by EMD. The anisotropic thermal conductivities of stoichiometric solid structures (Xe(He)₂ and Xe(He)₁₃) with different molar volume and atomic number are investigated, and results show that the thermal conductivities of Xe(He)₂ are more strongly anisotropic than those of Xe(He)₁₃, whereas the averaged thermal conductivities of Xe(He)₂ are around one tenth (1/10) of those of Xe(He)₁₃, indicating that the thermal conductivities of helium–xenon BNSLs (Xe(He)₂ and Xe(He)₁₃) significantly depend on the molecular structure in both magnitude and anisotropy. The results also show that both the magnitude and anisotropy of the thermal conductivity of helium–xenon BNSLs (Xe(He)₂ and Xe(He)₁₃) slightly depend on the atomic number and molar volume of the simulation system, with finite-size effects existing in the nanoscale system.