平衡态分子动力学Green-Kubo方法计算氮化硼单层结构热导率的模型尺寸效应研究

Effect of Domain Size on Thermal Conductivity of Boron Nitride Monolayer in Equilibrium Molecular Dynamics with Green-Kubo Method

分子动力学模拟可以直接表征体系原子的行为,因此成为研究氮化硼相关材料微观导热机理的重要工具,但目前尚没有关于氮化硼材料模型尺寸对其热传导相关性质影响规律的研究。该文采用平衡态分子动力学并结合Green-Kubo方法,研究了纯净氮化硼单层结构热导率、声子色散关系以及态密度随模拟尺寸的变化规律,并解释了其内部机理。实验发现,氮化硼单层材料热导率随着模拟尺寸的增大而减小,并在单层面积约4.1 nm×4.1 nm时收敛于(349±22)W/(m·K),此收敛值远小于平衡态分子动力学计算中石墨烯热导率的收敛尺寸(10 nm×10 nm),这说明氮化硼单层中声子之间的散射大于石墨烯。此外,不同于热导率,氮化硼单层结构的声子色散曲线、态密度几乎不受模拟尺寸的影响。该研究结果可为采用平衡态分子动力学研究氮化硼相关材料的微观导热机理提供重要参考。

Molecular dynamics simulation can directly model the molecular behavior, making it convenient to investigate the microscopic mechanism of thermal conductance of boron nitride （BN） nanomaterials. However, there still no explicitly investigation to the size effect of the BN monolayer on its thermal properties, in this paper, the equilibrium molecular dynamics （EMD） combined with the Green-Kubo method was used to unravel and explain the relations between the system size and the thermal conductivity, phonon dispersion, and phonon density of states （DOS） of pristine BN monolayer. It was found that the thermal conductivity of the BN monolayer decreased with increasing the size of the sturcture, reaching a converged value （349±22） W/（m.K） at 4.1 nm×4.1 nm. This value was much smaller than the converging size （10 nm×10 nm） of graphene in calculating its thermal conductivity using EMD simulations, which implied the phonon-phonon scattering in BN monolayer was larger than that in graphene. Different from the thermal conductivity, the phonon dispersion and phonon DOS of the BN monolayer did not depend on the size of the structure. Our findings provide important reference for investigating the microscopic mechanisms of BN related materials by using the equilibrium molecular dynamics modeling.