石墨转化纳米金刚石相变分子动力学模拟研究

Study on graphite to nano-diamond phase transition simulated by molecular dynamics method

为了探讨1维微尺度热传导模型不同激光能量对石墨转化纳米金刚石相变机理的影响,采用基于密度泛函理论的分子动力学方法模拟优化后的石墨结构,用有限差分法计算了激光辐照石墨表面的温度分布;基于sp^(3)杂化键可以明显地区分金刚石和石墨结构,根据能量耦合得到不同激光能量条件下辐照石墨的态密度带隙,研究了碳原子键合条件。结果表明,只有当激光能量达到5 J时,才能形成少量sp^(3)杂化碳原子;随着激光能量的增加,液相下受辐照的石墨表面的温度随之增加,碳原子中的自由电子更容易移动到成键分子轨道,电子的电负性增强,从而增强sp^(3)键的极性,并有助于将sp^(2)键转变为sp^(3)键。该研究结果对在液相激光辐照下提升纳米金刚石制备效率、探究纳米金刚石制备机理有重要的现实意义。

In order to discuss the influence of different laser energy on the transformation mechanism of graphite into nano-diamond in a 1-D microscale heat conduction model,optimized graphite structure was simulated by molecular dynamics method based on density functional theory(DFT).The temperature distribution of graphite surface irradiated by laser was calculated by the finite difference method.Based on the sp^(3) bond that can make a distinction between diamond and graphite was discussed especially,the carbon atom bonding condition was studied according to the band gap of the density of states(DOS)obtained by energy coupling.The results show that a small number of sp^(3) hybrid carbon atoms can be formed only when the laser energy reaches 5 J,and with the increase of laser energy,the temperature of the irradiated graphite surface in the liquid phase increases,the free electrons in the carbon atoms can be easier to move to a bonding molecular orbital,and the electronegativity of the electrons will be enhanced,which boosts the sp^(3) bond polarity and helps to transform sp^(2) bond into sp^(3) bond.This study has important practical significance in improving the preparation efficiency of nano-diamond under laser irradiation in the liquid phase and exploring the preparation mechanism of nano-diamond.