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The formalism of thermotransport in a binary system is analysed. Focus is put on a detailed consideration of the heat of transport parameter characterizing diffusion driven by a temperature gradient. We introduce the reduced heat of transport parameter Q Ã0 c , which characterizes part of the interdiffusion flux that is proportional to the temperature gradient. In an isothermal system Q Ã0 c represents the reduced heat flow (pure heat conduction) consequent upon unit interdiffusion flux. It is demonstrated that Q Ã0 c is independent of reference frame and is useful in a practical way for direct comparison of simulation and experimental data from different sources obtained in different reference frames. In the case study of the liquid Ni 50 Al 50 alloy, we use equilibrium molecular dynamics simulations in conjunction with the Green-Kubo formalism to evaluate the heat transport properties of the model within the temperature range of 1500-4000 K. Our results predict that in the presence of a temperature gradient Ni tends to diffuse from the cold end to the hot end whilst Al tends to diffuse from the hot end to the cold end.

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An analytical treatment of decomposition of the phonon thermal conductivity of a crystal with a monatomic unit cell is developed on the basis of a twostage decay of the heat current autocorrelation function observed in molecular dynamics simulations. It is demonstrated that the contributions from the acoustic short-and long-range phonon modes to the total phonon thermal conductivity can be presented in the form of simple kinetic formulas, consisting of products of the heat capacity and the average relaxation time of the considered phonon modes as well as the square of the average phonon velocity. On the basis of molecular dynamics calculations of the heat current autocorrelation function, this treatment allows for a self-consistent numerical evaluation of the aforementioned variables. In addition, the presented analysis allows, within the Debye approximation, for the identification of the temperature range where classical molecular dynamics simulations can be employed for the prediction of phonon thermal transport properties. As a case example, Cu is considered. IntroductionIt is well known that the thermodynamic and transport properties of a crystal lattice can be generally described using the concept of phonons (lattice vibrations or lattice waves) [1][2][3]. For example, the temperature dependence of the lattice heat capacity can be well accounted for within the harmonic approximation of the lattice vibrations by the Debye model [1]. In particular, the Debye model, in accordance with experiment, predicts that at high temperatures T [ T D (T D ¼ hx D =k B is the Debye temperature, x D is the Debye frequency -the highest allowed phonon frequency in the crystal, ℏ is the Planck constant divided by 2π, and k B is the Boltzmann constant), the lattice heat capacity can be approximated by the classical value C % 3Nk B =V (N is the number of atoms in the crystal volume V), which is known as Dulong and Petit value; whilst at low temperatures T \T D the lattice heat capacity starts to decrease (following C ∼ T 3 law at T ( T D ) which is a reflection of quantum effects on the phonon population [1].

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