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Ab initio molecular dynamics calculations of heat conductivity for silicon related materials DOI:10.15199/48.2017.08.16

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Thermal effects occurring in the active electronic elements and devices lead to their temperature increase and may change their functional characteristics. To keep these characteristics within the determined frameworks, one has to construct the corresponding devices taking into account the heat conductivity characteristics of the corresponding active and neighboring materials. Because of the large variety of these materials in modern electronics the problem of their heat characteristics determination is extremely important [1]. There are several theoretical techniques reported in the literature [2], which are used for determination of the phonon thermal conductivity. One of the often applied techniques is the molecular dynamics (MD), which can be separated into two main groups: (1) equilibrium and (2) nonequilibrium methods. In an equilibrium MD simulation, the system under investigation has a constant average temperature and an average heat flux of zero [2]. However, at each instant of time a finite heat flux exists due to instantaneous fluctuations of temperature. The popular Green-Kubo method [3, 4], based on the general fluctuation-dissipation theorem [5], relates the lattice thermal conductivity of the system to the time required for such fluctuations to dissipate. The corresponding algorithms however are not implemented in the more popular ab initio packages, for example in VASP code [6]. In the present study, we propose a new approach for the theoretical first-principles calculations of the phonon lifetime  and thermal diffusivity D of a material on the basis of the standard ab initio molecular dynamics (AMD) study. This approach has been applied to the study of heat conductivity in pure silicon and phosphorus doped silicon crystals. Some subsidiary calculations of this type were performed with diamond, sapphire (Al2O3) and silver. On the basis of the calculated thermal diffusivity D one can obtain the corr[...]

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