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RESEARCH PRODUCT

Semiquantum molecular dynamics simulation of thermal properties and heat transport in low-dimensional nanostructures

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We present a detailed description of the semi-quantum approach to the molecular dynamics simulation of stochastic dynamics of a system of interacting particles. Within this approach, the dynamics of the system is described with the use of classical Newtonian equations of motion in which the quantum effects are introduced through random Langevin-like forces with a specific power spectral density (the color noise). The color noise describes the interaction of the molecular system with the thermostat. We apply this technique to the simulation of the thermal properties of different low-dimensional nanostructures. Within this approach, we simulate the specific heat and heat transport in carbon nanotubes, as well as the thermal transport in a molecular nanoribbon with rough edges and in a nanoribbon with a strongly anharmonic periodic interatomic potential. We show that the existence of rough edges and quantum statistics of phonons change drastically the thermal conductivity of the rough-edge nanoribbon in comparison with that of the nanoribbon with ideal (atomically smooth) edges and classical dynamics. We show how the combination of strong nonlinearity of the interatomic potentials with quantum statistics of phonons changes the low-temperature thermal conductivity of the nanoribbon with periodic interatomic potentials. Molecular dynamics is a method of numerical modeling of molecular systems based on classical Newtonian mechanics. It does not allow for the description of pure quantum effects such as freezing out of high-frequency oscillations at low temperatures and the related decrease to zero of heat capacity for T → 0. In classical molecular dynamics, each dynamical degree of freedom possesses the same energy kBT, where kB is Boltzmann constant. Therefore, in classical statistics the specific heat of a solid almost does not depend on temperature when only relatively small changes, caused the anharmonicity of the potential, can be taken into account [1]). On the other hand, because of its complexity, a pure quantum-mechanical description does not allow in general the detailed modeling of the dynamics of many-body systems. To overcome these obstacles, different semiclassical methods, which allow to take into an account quantum effects in the dynamics of molecular systems, have been proposed [2–8]. The most convenient for the numerical modeling is the use of the Langevin equations with color-noise random forces [5, 7]. In this approximation, the dynamics of the system is described with the use of classical Newtonian equations of motion, while the quantum effects are introduced through random Langevin-like forces with a specific power spectral density (color noise), which describe the interaction of the molecular system with the thermostat. Below we give a detailed description of this semi-quantum approach, in application to the simulation of specific heat and heat transport in different low-dimensional nanostructures.