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Molecular Dynamics (MD) temperature versus Quantum Corrected temperature for graphene nanoribbon (GNR).
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The thermal conductivity of graphene nanoribbons (GNRs) has been investigated using equilibrium molecular dynamics (EMD) simulation based on Green-Kubo (GK) method to compare two interatomic potentials namely optimized Tersoff and 2nd generation Reactive Empirical Bond Order (REBO). Our comparative study includes the estimation of thermal conductiv...
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... Fig 9 represents the variation of obtained results of (8,0) and (12,0) SWCNTs employing EMD simulation for a wide range of 100� T(K) �1000. Our calculations for λ(T) with semiconducting and metallic SWCNTs without strains as a function of system T(K) are compared with the earlier results from MD simulations of Osman and Srivastava [8], EMD computations of Li et al., [36], and Khan et al., [37], GK homogeneous nonequilibrium MD (GK-HNEMD) of Zhang et al., [38], EMD and NEMD estimations of Berber et al., [27], and experimental investigations of Pop et al., [9] and Yoshino et al., [11]. The reported outcomes are in satisfactory agreement with earlier numerical and experimental investigations and illustrate that the current EMD simulations and previous GK-HNEMD and NEMD techniques have comparable efficiency, all producing nearly close values of λ(T). ...
Equilibrium molecular dynamics (EMD) simulations have been performed to investigate the structural analysis and thermal conductivity ( λ ) of semiconducting (8,0) and metallic (12,0) zigzag single-walled carbon nanotubes (SWCNTs) for varying ± γ (%) strains. For the first time, the present outcomes provide valuable insights into the relationship between the structural properties of zigzag SWCNTs and corresponding thermal behavior, which is essential for the development of high-performance nanocomposites. The radial distribution function (RDF) has been employed to assess the buckling and deformation understandings of the (8,0) and (12,0) SWCNTs for a wide range of temperature T (K) and varying ± γ (%) strains. The visualization of SWCNTs shows that the earlier buckling and deformation processes are observed for semiconducting SWCNTs as compared to metallic SWCNTs for high T (K) and it also evident through an abrupt increase in RDF peaks. The RDF and visualization analyses demonstrate that the (8,0) SWCNTs can more tunable under compressive than tensile strains, however, the (12,0) zigzag SWCNTs indicate an opposite trend and may tolerate more tensile than compressive strains. Investigations show that the tunable domain of ± γ (%) strains decreases from (-10%≤ γ ≤+19%) to (-5%≤ γ ≤+10%) for (8,0) SWCNTs and the buckling process shifts to lower ± γ (%) for (12,0) SWCNTs with increasing T (K). For intermediate-high T (K), the λ ( T ) of (12,0) SWCNTs is high but the (8,0) SWCNTs show certainly high λ ( T ) for low T (K). The present λ ( T , ± γ ) data are in reasonable agreement with parts of previous NEMD, GK-HNEMD data and experimental investigations with simulation results generally under predicting the λ ( T , ± γ ) by the ∼1% to ∼20%, regardless of the ± γ (%) strains, depending on T (K). Our simulation data significantly expand the strain range to -10% ≤ γ ≤ +19% for both zigzag SWCNTs, depending on temperature T (K). This extension of the range aims to establish a tunable regime and delve into the intrinsic characteristics of zigzag SWCNTs, building upon previous work.
... Green-Kubo (GK) method [41,42] is one of the popularly used numerical schemes under for the calculation of thermal conductivity based on fluctuation-dissipation theory. One of the major advantages of the GK method is that it is stable and less size dependent than the NEMD approach [43][44][45][46][47]. Besides, it provides all the 2nd-order tensor components. ...
Layered minerals containing inter-layer water show directional anisotropy. In previous work, the authors have shown that this inter-layer water affects the mechanical performance of these minerals. Even though difference in thermal conductivity of minerals has been alluded to in experimental literature due to presence of water molecules within crystal, a detailed coordinated theoretical study has not been carried out. In this work, a molecular dynamics study has been presented on sulfates of calcium to demonstrate that thermal conductivity is indeed reduced with the presence of inter-layer water. The correlation between the vibration of different molecular groups to the thermal transport mechanism of the material has been investigated. It has been observed that vibration modes of H 2 O molecules have a negligible contribution to thermal transport eventually reducing thermal conductivity perpendicular to the water layer. Even though calcium sulfate has been chosen for this study, it can be anticipated that similar behaviors can be observed with other minerals in which inter-layer water is present. This study represents a detailed structure-property correlation in the thermal transport mechanism through layered minerals.
... Green-Kubo (GK) method [41,42] is one of the popularly used numerical schemes under for the calculation of thermal conductivity based on fluctuation-dissipation theory. One of the major advantages of the GK method is that it is stable and less size dependent than the NEMD approach [43][44][45][46][47]. Besides, it provides all the 2nd-order tensor components. ...
Layered minerals containing inter-layer water show directional anisotropy. In previous work, the authors have shown that this inter-layer water affects the mechanical performance of these minerals. Even though difference in thermal conductivity of minerals has been alluded to in experimental literature due to presence of water molecules within crystal, a detailed coordinated theoretical study has not been carried out. In this work, a molecular dynamics study has been presented on sulfates of calcium to demonstrate that thermal conductivity is indeed reduced with the presence of inter-layer water. The correlation between the vibration of different molecular groups to the thermal transport mechanism of the material has been investigated. It has been observed that vibration modes of H 2 O molecules have a negligible contribution to thermal transport eventually reducing thermal conductivity perpendicular to the water layer. Even though calcium sulfate has been chosen for this study, it can be anticipated that similar behaviors can be observed with other minerals in which inter-layer water is present. This study represents a detailed structure-property correlation in the thermal transport mechanism through layered minerals.
... In the case of temperature, the value remains stable around the temperature set in the starting conditions (300 K), while for its part, the volume of the system suffers a slight contraction from the values set in the starting conditions. From 42 nm 3 to an average value of around 36.5 nm 3 ; this contraction is a direct consequence of the pressure coupling process using Berensen's algorithm [33]. ...
The adsorption of methylene blue on different adsorbents has been widely studied due to the most common textile contaminant in waters. In this work, methylene blue adsorption onto graphene obtained from rice husks was studied experimentally and theoretically. Graphene was prepared by alkaline calcining solid mixture, in the absence of oxygen. Graphene was characterized by UV–visible and infrared absorption spectroscopy, atomic force microscopy, dynamic light scattering, and scanning electron microscopy. The adsorption isotherm was performed under standard temperature conditions. The experimental data indicated that graphene has good adsorbent qualities; the maximum adsorption capacity was 100 mg/g, the equilibrium constant of the process 1.44 ± 0.03, and the Gibbs free energy of 92.3 ± 0.2 kJ/mol, which shows that the adsorption is spontaneous and strongly favored. In addition, the surface active area of the material is 7826 ± 3 m²/g. The experimental results were compared with theoretical using molecular dynamics (MD) to study the nature of different interactions involved in the adsorption of dye molecules onto graphene sheets. The computational simulation resulted in an adsorption energy of (− 132 ± 13) KJ/mol. Equilibrium configurations obtained from MD simulations confirmed that the predominant interactions are π−π Lennard–Jones type. The results suggest that the methylene blue molecule acquires coplanar configurations with the graphene sheet and the analysis of the radial density function (RDF) revealed that the interaction is stronger in the aromatic portion of the dye molecule compared to the aliphatic groups.
... Quantum correction for thermal conductivity calculations of classical MD is required because quantum effects in classical MD approximation below the Debye temperature (T d ) are neglected [25,26]. To investigate the thermal conductivity at low temperatures, it is necessary to find the specific heat capacity using PDOS [27]. ...
Twisted bilayer graphene (tBLG) is two graphene layers placed on top of each other with a twist angle, making it has tunable thermal properties. In this paper, we report an analysis of thermal conductivity ($\kappa$), phonon density of states, and specific heat capacity of tBLG with various twist angles over a range of temperatures using equilibrium molecular dynamics simulations based on the Green-Kubo method. Simulation shows that stacking and twisting graphene layers lead to a decrease in the thermal conductivity, with the highest $\kappa$ at around room temperature owned by the tBLG with a twist angle of 3.89$^{\circ}$ followed by 16.43$^{\circ}$ and 4.41$^{\circ}$. We also perform quantum correction to the simulation results to show the process of increasing thermal conductivity at low temperatures.
... In order to fit our simulation results, we borrow the Einstein specific heat and the Mean Free Path (MFP) from the Einstein model, take v as E/ρ and replace them in Equation (2), thereby, obtaining a modifying version of Equation (3): Figure 8 shows the results for the thermal conductivity of NW with a radius of 2 nm and different sp 3 content, including a comparison with the Einstein conductivity model, Equations (3) and (6). As Figure 8 show, quantum corrections would be significant only below the Debye temperature [90,91]. Conductivity is roughly constant with temperature and increases with sp 3 content, as expected. ...
The thermal conductivity of nanostructures can be obtained using atomistic classical Molecular Dynamics (MD) simulations, particularly for semiconductors where there is no significant contribution from electrons to thermal conduction. In this work, we obtain and analyze the thermal conductivity of amorphous carbon (aC) nanowires (NW) with a 2 nm radius and aC nanotubes (NT) with 0.5, 1 and 1.3 nm internal radii and a 2 nm external radius. The behavior of thermal conductivity with internal radii, temperature and density (related to different levels of sp3 hybridization), is compared with experimental results from the literature. Reasonable agreement is found between our modeling results and the experiments for aC films. In addition, in our simulations, the bulk conductivity is lower than the NW conductivity, which in turn is lower than the NT conductivity. NTs thermal conductivity can be tailored as a function of the wall thickness, which surprisingly increases when the wall thickness decreases. While the vibrational density of states (VDOS) is similar for bulk, NW and NT, the elastic modulus is sensitive to the geometrical parameters, which can explain the enhanced thermal conductivity observed for the simulated nanostructures.
... Various theoretical calculation methods such as molecular dynamics simulation [14][15][16][17], phonon Boltzmann transport equation [18][19][20][21][22][23], and atomistic Green's functions [24][25][26] have been developed to study the underlying physical mechanism of heat transfer in 2D materials. Yet, due to the ignorance of surface defects, the accuracy of these methods is limited. ...
... In addition, the phonon scattering rate in MD is related to the Maxwell Boltzmann distribution while ignoring the quantum effect below the Debye temperature. Thus, erroneous results were obtained for the calculated thermal conductivity below the Debye temperature [17]. ...
Two-dimensional (2D) materials are widely used in microelectronic devices due to their excellent optical, electrical, and mechanical properties. The performance and reliability of microelectronic devices based 2D materials are affected by heat dissipation performance, which can be evaluated by studying the thermal conductivity of 2D materials. Currently, many theoretical and experimental methods have been developed to characterize the thermal conductivity of 2D materials. In this paper, firstly, typical theoretical methods, such as molecular dynamics, phonon Boltzmann transport equation, and atomic Green’s function method, are introduced and compared. Then, experimental methods, such as suspended micro-bridge, 3ω, time-domain thermal reflectance and Raman methods, are systematically and critically reviewed. In addition, the physical factors affecting the thermal conductivity of 2D materials are discussed. At last, future prospects for both theoretical and experimental thermal conductivity characterization of 2D materials is given. This paper provides an in-depth understanding of the existing thermal conductivity measurement methods of 2D materials, which has guiding significance for the application of 2D materials in micro/nanodevices.
... 59 . Thermal conductivity was calculated using the equilibrium Green-Kubo formalism 60,61 . A monolayer MoSe 2 flake of 2.3 by 2.3 nm was first equilibrated with an NVT ensemble for 0.1 ns, followed by an NVE step of 1 ns during which the ensemble average of the autocorrelation of the heat flux was measured for calculating the thermal conductivity. ...
This investigation presents a generally applicable framework for parameterizing interatomic potentials to accurately capture large deformation pathways. It incorporates a multi-objective genetic algorithm, training and screening property sets, and correlation and principal component analyses. The framework enables iterative definition of properties in the training and screening sets, guided by correlation relationships between properties, aiming to achieve optimal parametrizations for properties of interest. Specifically, the performance of increasingly complex potentials, Buckingham, Stillinger-Weber, Tersoff, and modified reactive empirical bond-order potentials are compared. Using MoSe2 as a case study, we demonstrate good reproducibility of training/screening properties and superior transferability. For MoSe2, the best performance is achieved using the Tersoff potential, which is ascribed to its apparent higher flexibility embedded in its functional form. These results should facilitate the selection and parametrization of interatomic potentials for exploring mechanical and phononic properties of a large library of two-dimensional and bulk materials.
... Moreover, charge carriers in silicene exhibit linear Dirac dispersion relation with ultrahigh Fermi velocity thereby reflecting the excellent electronic properties of silicene [13,14]. On the other hand, recent studies have reported a low thermal conductivity of monolayer silicene (5.5-20 W/m/K) [15] at room temperature compared to other materials such as graphene [16] and bulk silicon (150-200 W/m/K) [14]. The low thermal conductivity of silicene in combination with its excellent electronic properties suggests the possibility of using silicene based nanostructures in the design of efficient thermoelectrics [17]. ...
The compatibility of silicene with the semiconductor technology and its promise in thermoelectric and in op-toelectronic devices demands modulation and optimization of its thermal and optical properties using structural modifications. Here we investigate the thermal and optical properties of silicene supported group IV honeycomb bilayer and heterobilayer nanoribbon structures (silicene/germanene and silicene/graphene) using molecular dynamics simulation and first principle calculations. Our modeled silicene/germanene nanoribbons show ~43% lower room temperature average thermal conductivity (2.94 W/m/K) compared to that of similar sized silicene nanoribbons (5.1 W/m/K). Similarly, in silicene/graphene nanoribbons, heterostructuring results in a ~25× reduction of the in-plane thermal conductivity compared to that of a graphene nanoribbon, which is attributed to the phonon confinement in the low frequency region and large mismatch in the phonon frequencies between the monolayers of these heterostructures (~50 THz for the graphene layer and ~11 THz for the silicene layer in the silicene/graphene nanoribbons). We also characterize the temperature and the size dependent thermal conductivity of the modeled structures. The realized low thermal conductivity in these heterostructures could lead to the design of optimized thermoelectrics. Furthermore, we compute the frequency dependent dielectric function and show that the absorption coefficients of our modeled nanostructures are 1.5× to 2× large compared to those of silicene monolayer in the ultraviolet (UV) region, which could be useful in optoelectronic devices such as UV photodetectors. Thus, heterostructuring could be an encouraging route to tune the thermal and optical properties of silicene nanostructures for next generation nano-electronic and optoelectronic devices.
... When the temperature was varied from 100 K to 600 K, the TC was reduced by ~53%, from ~27.3 W/m.K to ~12.9 W/m.K. A similar decrease in TC was also observed in previous studies for graphene and silicon nanomaterials [76][77][78]. Such drooping characteristic of TC with increasing temperature can be explained by the reduction of MFP and group velocity of phonons by various phonon scattering mechanisms at elevated temperatures [79]. ...
... Computational Materials Science 191 (2021) 110338 to the excitement of more and more high-frequency phonon modes, that is, the increase in the population of energy carrier [58]. This might also occur as a result of the enhanced non-linear thermal resistivity resulting from the anharmonic interactions of phonons at extremely high temperatures by higher-order (three-phonon and four-phonon) scattering processes [78,85]. ...
Silicene has recently grabbed tremendous attention in the scientific community owing to its superb electronic and thermal properties and the promise of high-efficiency thermoelectric operations. Notwithstanding rigorous analyses of its electronic properties, little attention has been paid so far to explore and tailor the thermal transport characteristics of silicene. This study employed optimized Tersoff potential to extensively investigate the thermal conductivity (TC) of pristine and defective silicene using non-equilibrium molecular dynamics (NEMD) simulations. We analyzed the influence of temperature variation, percentage of carbon doping, and monovacancy concentration on the phonon TC along both armchair and zigzag directions and elucidated the underlying mechanisms that modulate these effects. The simulation results reveal excellent isotropic behavior of the material in the considered temperature regime. Our predicted room-temperature TC of pristine silicene of ~ 20 W/m.K shows excellent conformity with prior studies. Simulation results suggest that the TC deteriorates significantly with increasing concentration of carbon doping. It is revealed that incorporating only 5% of carbon dopants can reduce the TC of silicene by ~ 71%. Meanwhile, with the increase in temperature from 100 K to 600 K, the thermal conductivities of both pristine and carbon-doped silicene are also found to decline dramatically by ~14 W/m.K and ~9 W/m.K, respectively. The vacancy defect study reveals that thermal conductivities of both pure and carbon-doped silicene are also a strong function of vacancy concentration and can be reduced by ~ 58% by removing only 1% of silicon atom from the pristine nanosheet. It is further disclosed that the impact of vacancy on regulating the TC is more pronounced in pristine silicene than the carbon-doped silicene. To obtain a detailed insight into the thermal transport mechanism, phonon density of states (PDOS) is computed using the fast Fourier transform of the atomic velocity autocorrelation function. The PDOS discloses interesting phonon spectrum features under impurity doping, temperature variation, and increased vacancy concentration. Overall, this study offers a comprehensive roadmap for engineering the thermal conductivity of silicene and will grease the wheels for designing efficient thermal management systems for the present silicon-based semiconductor industry.
