The molecular dynamics on the concentration fluctuations and the mutual diffusion coefficient in the supercritical solution

对超临界区Lennard-Jones混合物进行了分子动力学模拟。第一个分量是Ar，另一个分量是Kr，对这两种情况进行了模拟。第一个是二维系统，在给定分子数的单位细胞中，细胞长度比三维情况下更长。另一个系统是3d系统。在后一种情况下，单元胞中的分子数为23328，摩尔分数为0.5。在临界点附近的浓度波动与两种体系的理想混合相比较大。运动学因子由构件1质心的均方位移得到。根据Kirkwood-Buff理论，用径向分布函数计算热力学因子。互扩散系数是运动因子和热力学因子的乘积。由自扩散系数归一化的互扩散系数在临界密度附近由于浓度波动较大，值较小。比较了超临界区密度和浓度的热容、偏摩尔体积和相关长度。

Molecular dynamics simulations on Lennard-Jones mixture in the supercritical region are performed. The first component is Ar and the other one is Kr. The simulations are done in the two cases. The first one is a 2-D system, where the cell length is longer for a given molecule number in the unit cell compared to that in the 3-D case. The other system is the 3-D one. In the later case, the number of the molecule in the unit cell is 23328 and the mole fraction is 0.5. The concentration fluctuations near the critical point are large compared to the ideal mixing in the both systems.The kinematic factor is obtained by the mean square displacement of the center of mass of the component 1. The thermodynamic factor is calculated by the radial distribution functions according to the Kirkwood-Buff theory. The mutual difusion coefficient is the product of the kinematic factor and thermodynamic one.The normalized mutual diffusion coefficient by the self-diffusion coefficient has small value near the critical density because of the large concentration fluctuation. The heat capacity, partial molar volume and correlation lengths of density and concentration in the supercritical region are compared with those at the normal density.