石墨烯热膨胀系数的尺寸效应研究

Study on the Scale Effect of Graphene's Coefficient of Thermal Expansion

采用分子动力学模拟的方法,对单层石墨烯的面热膨胀系数进行了研究。结果发现,单层石墨烯的面热膨胀系数随温度的变化呈非线性变化,且在0~1 200 K的温度范围内是负值(热收缩)。重点研究了石墨烯的面热膨胀系数与模型尺寸和采样区域尺寸的关系,结果表明,1)当石墨烯模型尺寸小于10.0 nm×10.0 nm时,随着模型尺寸的增大石墨烯的面热膨胀系数绝对值变小,当模型尺寸大于或等于10.0 nm×10.0 nm时,随着模型尺寸的增大石墨烯的面热膨胀系数无明显变化,处在一定的分布带内;2)采样区域尺寸过小会导致石墨烯的面热膨胀系数结果不稳定,不易收敛,当采样区域大于一定尺寸后则可得到稳定的热膨胀系数,并且易收敛,为此提出了较为合理的采样区域尺寸。

The coefficient of superficial thermal expansion （α） of single layer graphene （SLG） was studied through molecular dynamics （MD） simulation. Results show that a values of SLG varies nonlinearly with the change of temperature, and it is negative in the temperature range of 0 - 1 200 K （thermal contraction）. The relationship between the model size and the sampling area size and α was studied intensively. The results show that： on the one hand, when the model size is smaller than 10. 0 nm×10. 0 nm, the absolute value of α decreases with the increase of the model size ; when the model size is not smaller than 10. 0 nm×10. 0 nm, it does not change apparently with the increasing model size and keeps in a certain distribution; on the other hand, a too small sampling area will lead to unstable coefficient of superficial thermal expansion and it is hard to obtain convergent α results; when the sampling area is larger than a certain value, stable and convergent α results can be achieved. Based on this, reasonable sampling area in the coefficient of superficial thermal expansion study of SLG is suggested.