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Simulation studies of ionic liquids: Orientational correlations and static dielectric properties

机译:离子液体的模拟研究:方向相关性和静态介电特性

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The ionic liquids BMIM+I-, BMIM+BF4-, and BMIM+PF6- were simulated by means of the molecular dynamics method over a time period of more than 100 ns. Besides the common structural analysis, e.g., radial distribution functions and three dimensional occupancy plots, a more sophisticated orientational analysis was performed. The angular correlation functions g(00)(110)(r) and g(00)(101)(r) are the first distance dependent coefficients of the pairwise orientational distribution function g(r(ij),Omega(1),Omega(2),Omega(12)). These functions help to interpret the three dimensional plot and reveal interesting insights into the local structure of the analyzed ionic liquids. Furthermore, the collective network of ionic liquids can be characterized by the Kirkwood factor G(kappa)(r) [J. Chem. Phys. 7, 911 (1939)]. The short-range behavior (r < 10 A) of this factor may be suitable to predict the water miscibility of the ionic liquid. The long-range limit of G(k)(infinity) is below 1 which demonstrates the strongly coupled nature of the ionic liquid networks. In addition, this factor relates the orientational structure and the dielectric properties of the ionic liquids. The static dielectric constant epsilon(omega=0) for the simulated system is 8.9-9.5. Since in ionic liquids the very same molecule contributes to the total dipole moment as well as carries a net charge, a small, but significant contribution of the cross term between the total dipole moment and the electric current to epsilon(omega=0) is observed. (c) 2006 American Institute of Physics.
机译:通过分子动力学方法在超过100 ns的时间段内模拟了离子液体BMIM + I-,BMIM + BF4-和BMIM + PF6-。除了常见的结构分析(例如径向分布函数和三维占用图)以外,还执行了更复杂的定向分析。角度相关函数g(00)(110)(r)和g(00)(101)(r)是成对取向分布函数g(r(ij),Omega(1),Omega的第一距离相关系数(2),欧米茄(12))。这些功能有助于解释三维图,并揭示对所分析的离子液体的局部结构的有趣见解。此外,离子液体的集合网络可以用柯克伍德因子G(kappa)(r)来表征。化学物理7,911(1939)]。该因素的短程行为(r <10 A)可能适合预测离子液体的水混溶性。 G(k)(无穷大)的远程极限小于1,这表明离子液体网络的强耦合性质。另外,该因素与离子液体的取向结构和介电性能有关。模拟系统的静态介电常数ε(ω= 0)为8.9-9.5。由于在离子液体中,完全相同的分子会贡献总偶极矩并带有净电荷,因此观察到总偶极矩与电流之间的交叉项对ε的贡献很小,但有很大贡献(ω= 0) 。 (c)2006年美国物理研究所。

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