Collective excitations in an ionic liquid.
Collective excitations in an ionic liquid.
复制标题
离子液体中的集体激发。
DOI：
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发表时间：
2006
影响因子：
4.4
通讯作者：
M. Ribeiro
中科院分区：
文献类型：
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作者：
S. Urahata;M. Ribeiro
分子动力学模拟揭示了离子液体代表性模型，即氯化1-丁基-3-甲基咪唑鎓的集体动力学。在波矢量范围 0.17 < k < 1.40 埃(-1) 内获得了纵向声学 (LA) 和横向声学 (TA) 模式的能量激励色散，即 omega 与 k 的关系，该范围包含静态结构因子 S(k) 的主峰。观察到声学模式的线性色散高达 k 约 0.7 埃(-1)。由于 LA 和 TA 模式之间的混合，LA 光谱显示出类横向分量，反之亦然。由于短时离子动力学的各向异性，当阳离子位移沿咪唑环平面或垂直于咪唑环平面投影时，声学模式在高 k 时实现不同的限制 omega 值。在充电电流光谱中，欧米茄与 k 的负色散分支是模拟离子液体中光学模式的特征。使用Nernst-Einstein方程中的离子扩散系数估算的电导率kappa高于通过积分充电电流相关函数计算的实际kappa。根据 TA 谱，评估了波矢量相关的粘度 eta(k)，其低 k 极限给出了 eta 与实验数据的合理一致。
Collective dynamics in a representative model of ionic liquids, namely, 1-butyl-3-methylimidazolium chloride, have been revealed by molecular dynamics simulation. Dispersion of energy excitation, omega versus k, of longitudinal acoustic (LA) and transverse acoustic (TA) modes was obtained in the wave vector range 0.17 < k < 1.40 Angstroms(-1), which encompasses the main peak of the static structure factor S(k). Linear dispersion of acoustic modes is observed up to k approximately 0.7 Angstroms(-1). Due to mixing between LA and TA modes, LA spectra display transverselike component, and vice versa. Due to anisotropy in short-time ionic dynamics, acoustic modes achieve distinct limiting omega values at high k when the cation displacement is projected either along the plane or perpendicular to the plane of the imidazolium ring. In charge current spectra, branch with negative dispersion of omega versus k is a signature of optic modes in the simulated ionic liquid. Conductivity kappa estimated by using ionic diffusion coefficients in the Nernst-Einstein equation is higher than the actual kappa calculated by integrating the charge current correlation function. From TA spectra, a wave vector dependent viscosity eta(k) has been evaluated, whose low-k limit gives eta in reasonable agreement with experimental data.