Yamaguchi T, Matsuoka T, Koda S
Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa, Nagoya, Aichi 464-8603, Japan.
J Chem Phys. 2005 Jan 1;122(1):14512. doi: 10.1063/1.1828039.
The transient response function of the density profile of the solvent around a solute during the translational diffusion of the solute is formulated based on the generalized Langevin formalism. The resultant theory is applied to both neat Lennard-Jones fluids and cations in liquid water, and the response functions are obtained from the analysis of the molecular dynamics simulations. In the case of the self-diffusion of Lennard-Jones fluids, the responses of the solvation structures are in harmony with conventional pictures based on the mode-coupling theory, that is, the binary collision in the low-density fluids, the backflow effect from medium to high density fluids, and the backscatter effect in the liquids near the triple point. In the case of cations in water, the qualitative behavior is strongly dependent on the size of cations. The pictures similar to simple dense liquids are obtained for the large ion and the neutral molecule, while the solvent waters within the first solvation shell of small ions show an oscillatory response in the short-time region. In particular, the oscillation is remarkably underdumped for lithium ion. The origin of the oscillation is discussed in relation to the theoretical treatment of the translational diffusion of ions in water.
基于广义朗之万形式理论，推导了溶质平动扩散过程中溶质周围溶剂密度分布的瞬态响应函数。所得理论应用于纯 Lennard-Jones 流体和液态水中的阳离子，并通过分子动力学模拟分析获得响应函数。在 Lennard-Jones 流体的自扩散中，溶剂化结构的响应与基于模式耦合理论的传统图像一致，即在低密度流体中的二元碰撞、从中密度到高密度流体的回流效应以及在三相点附近液体中的后向散射效应。在水中阳离子的情况下，定性行为强烈依赖于阳离子的大小。对于大离子和中性分子，得到了类似于简单致密液体的图像，而小离子第一溶剂化壳层内的溶剂水分子在短时间区域表现出振荡响应。特别是，锂离子的振荡明显欠阻尼。结合水中离子平动扩散的理论处理，讨论了振荡的起源。
