石墨烯热膨胀系数的尺寸效应研究

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。

Elastic and thermodynamic properties of TiC from first-principles calculations

Using the pseudopotential plane-wave method, we investigate the elastic constants and thermodynamic properties of the rocksalt structure Titanium Carbide (TiC). The obtained lattice parameters, bulk modulus and elastic constants are in very good agreement with the available experimental data and other theoretical results. The thermodynamic properties of the cubic TiC are predicted by using the quasi-harmonic Debye model. The normalized volume V/V 0 , bulk modulus B, thermal expansion , heat capacity C V , Grüneisen parameter and Debye temperature dependence on the pressure and temperature are obtained successfully. At low temperature and low pressure, thermal expansion coefficient increases rapidly with temperature. At high temperature and high pressure, the increasing trend becomes tender. At low temperatures, C V is proportional to T 3 , and C V tends to the Dulong-Petit limit at higher temperatures.