The thermal conductivity of graphene nanoribbons (layer from 1 to 8 atomic planes) is investigated by using the nonequilibrium molecular dynamics method. We present that the room-temperature thermal conductivity decays monotonically with the number of the layers in few-layer graphene. The superiority of zigzag graphene in thermal conductivity is only available in high temperature region and disappears in multi-layer case. It is explained that the phonon spectral shrink in high frequency induces the change of thermal conductivity. It is also reported that single-layer graphene has better ballistic transport property than the multi-layer graphene.In the past decade, more and more attentions have been given to the question of what happens with thermal conductivity when goes to low-dimensional materials [1]. A two-dimensional materials-graphene [2], in addition to its exceptional electric [3] and optical properties [4] , [5], reveals unique high thermal conductivity. Thermal conductivity of single-layer graphene as well as of carbon nanotubes is dependent on the chirality [6]. Recent theoretical studies suggest that the thermal conductivity of single-layer zigzag graphene is 20-50% larger than that of the singlelayer armchair graphene [7]. However, whether the superior thermal conductivity of zigzag graphene remains available for multi-layer graphene has not got enough attention and concern.Additionally, experimental demonstrations have shown that the thermal conductivity gets a decrease at the twoto three-dimensional (2D to 3D) crossover of few-layer graphene [8]. The fact that the thermal conductivity of large enough graphene sheets should be higher than that of basal planes of bulk graphite was predicted theoretically by Klemens [9]. Generally, thermal transport in conventional thin films still retains 'bulk' features because the crosssections of these structures are measured in many atomic layers. Heat conduction in such nanostructures is dominated by extrinsic effects, for example, phonon-boundary or phonon-defect scattering [10]. A recent experimental observation of high-quality few-layer graphene materials shows that the room-temperature thermal conductivity changes from˜2,800 to˜1,300 Wm −1 K −1 when the number of atomic planes in few-layer graphene increases from 2 to 4. It is explained that the observed evolution from two dimensions to bulk attributed to the cross-plane coupling of the low-energy phonons and changes in the phonon Umklapp scattering [8].Recently, the method of molecular dynamics simulation has been successful in discovering thermal conductivity and thermal rectification of the nanostructures [7] , [11]. This method, which builds the system from the bottom up, is useful to understand the intrinsic behavior, i.e., the phonon spectral behavior behind the significant change of a material's ability to conduct heat [12]. In this paper, we will study the thermal conductivity of graphene ribbons (layer from 1 to 8 atomic planes) by using the nonequilibrium molecular dynamics method. By inve...

A two-segment Fermi-Pasta-Ulam lattices has been investigated by using nonequilibrium molecular dynamics. Here we present an anomalous negative differential thermal resistance (NDTR) that have not been reported in Frenkel-Kontorova and φ 4 lattices up to the present. The NDTR disappears at low temperature region. The region of NDTR shifts from the large to the small temperature difference region as the system size increases. Anomalous dependence of NDTR on the temperature can be explained as the negative effect induced by the nonlinear coupling. The explanation can also cover the phenomenon of NDTR in momentum-nonconserved lattices.

We investigate the thermal conductivity of four types of deformed carbon nanotubes by using the nonequilibrium molecular dynamics method. It is reported that various deformations have different influence on the thermal properties of carbon nanotubes. For the bending carbon nanotubes, the thermal conductivity is independent on the bending angle. However, the thermal conductivity increases lightly with XY-distortion and decreases rapidly with Z-distortion. The thermal conductivity does not change with the screw ratio before the breaking of carbon nanotubes but decreases sharply after the critical screw ratio.Comment: 6figure

Enhancement effect of asymmetry on the thermal conductivity of double-stranded chain systems *Zhang Mao-Ping( ) a) , Zhong Wei-Rong( ) a) † , and Ai Bao-Quan( ) b)

Using nonequilibrium molecular dynamics simulation, we study the thermal rectification of an asymmetric double-stranded molecular structure system. We investigate the influence of temperature, intra- and inter-chain interaction and the system size on the thermal rectification effect of the asymmetric double- chain system. It is reported that the intra- and the inter-chain interaction have an advantage on the rectification efficiency. The rectification efficiency goes to a stable value at a large system size. This phenomenon is also explained by the power spectra of the inter-particles, which is similar to the situation of the single chain system.