分子动力学模拟超临界水微观结构及自扩散系数

Microstructure and self-diffusion coefficient of supercritical water by molecular dynamics simulation

采用分子动力学模拟方法,选用COMPASS力场,对超临界水的微观结构和扩散系数进行了研究。结果表明,在超临界区水分子的氢键作用明显减弱,但是仍有氢键存在。水分子的键长和键角在温度为648～748 K时变化迅速,在温度为748～973 K时变化很小。径向分布函数特征峰值在温度为648～748 K时随温度的升高而增大,在温度为748～973 K时随温度升高而减小,表明水分子近程结构有序性随温度变化。超临界水自扩散系数是常温常压水的2个数量级,随温度升高而增大,随压力的升高而减小。

By using molecular dynamics simulation with COMPASS force field, microstructure and self-diffusion coefficient of supercritical water were researched. The results show that the effect of the hydrogen bond on supercritical water is weakened obviously, and still exist. The bond length and the bond angle of the water molecular changed rapidly in the region of 648-748 K. The bond length and the bond angle of the water molecular changed slowly in 748-973 K. The characteristic peaks of radial distribution function increased with the increase of temperature in the region of 648 ~748 K, and decreased with the increase of temperature in the region of 748-973 K, which indicated that short range structure orderliness of water was changing with the increase of temperature. The self-diffusion coefficients of supereritical water were two orders of magnitude higher than ＇ambient water, and increased with the increase of temperature, decreased with the increase of pressure.