Interfacial thermal resistance (ITR) in bi-layer nanofilms is investigated by nonequilibrium molecular dynamics simulation. The relationships among ITR, interfacial temperature, film thickness, heat flux direction and film materials are investigated. The ITR is found to become lower with increasing interfacial temperature, and film thickness has no obvious influence on ITR in the range of the simulation layer thickness. ITR is found to be dependent on the heat flux direction and layer materials. Analyses of heat flux direction and layer materials based on phonon density of states (DOS) indicate that the mismatch of DOS of each layer is the main cause of interfacial resistance and the frequency distribution of DOS also affects interfacial resistance.
We extend the recently proposed Z method of estimating the melting temperature from a complete liquid and propose a modified Z method to calculate the melting temperature from a solid-liquid coexistence state. With the simulation box of rectangular parallelepiped, an initial structure of perfect lattice can run in the microcanonical ensemble to achieve steady solid-liquid coexistence state. The melting pressure and temperature are estimated from the coexistence state. For the small system with 1280 atoms, the simulation results show that the melting curve of copper has a good agreement with the experiments and is identical in accuracy with the results of the two-phase coexistence method with 24 000 atoms in the literature. Moreover, the method is conceptually simpler than the two-phase coexistence method.
A nonequilibrium molecular dynamics study of the cross-plane thermal conductivity and interfacial thermal resistance of nanoscale bilayered films is presented. The films under study are composed of argon and another material that is identical to argon except for its atomic mass. The results show that a large temperature jump occurs at the interface and that the interfacial thermal resistance plays an important role in heat conduction for the whole films. The cross-plane thermal conductivity is dependent on the average temperature. The interfacial thermal resistance is found to be dependent apparently on the atomic mass ratio of the two materials and the temperature, but to be independent of the film thickness. A linear relationship is observed between the reciprocal of the cross-plane thermal conductivity and that of the film thickness with the film thickness between 5.4 nm and 64.9 nm, which is in good agreement with results in the literature for a single film.
We examined the validity of the modified Z method to predict the high-pressure melting curve of the body-centered-cubic transition metals, e.g., tantalum, in the molecular dynamics simulations using an extended Finnis-Sinclair potential. A unique feature was observed that a solid system evolves into the steady interphase of the solid and the liquid. In spite of simple running processes, the melting curve extracted from the solid-liquid coexistence states composed of only 960 atoms reaches an excellent agreement with that of the two-phase method in the literature. The liquid microstructure at the melting curve is dominated by the icosahedral short-range order, almost independent of the pressure up to 400 GPa.
The shear viscosity of matter and efficient simulating methods in a wide range of temperatures and densities are desirable. In this study, we present the deep-learning many-body potential (the deep potential) method to reduce the computational cost of simulations for the viscosity of liquid aluminum at high temperature and high pressure with accurate results. Viscosities for densities of 2.35 g/cm3, 2.7 g/cm3, 3.5 g/cm3, and 4.27 g/cm3 and temperatures from melting points to about 50 000 K are calculated. The results agree well with the experiment data at a pressure near 1 bar and are consistent with the simulation of first-principles at high pressure and high temperature. We reveal the behavior of the shear viscosity of liquid Al at a range where the current experimental results do not exist. Based on the available experimental data and newly generated simulation data, we propose a modified Enskog–Dymond theory, which can analytically calculate the viscosity of Al at this range. This research is helpful for numerous potential applications.
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