三乙铵三氟甲磺酸质子离子液体的密度泛函计算和分子动力学模拟,The Journal of Physical Chemistry B

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三乙铵三氟甲磺酸质子离子液体的密度泛函计算和分子动力学模拟
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2017-12-11 00:00:00 , DOI: 10.1021/acs.jpcb.7b10373
Juan F. Mora Cardozo ₁ , T. Burankova ₁ , J. P. Embs ₁ , A. Benedetto _{1,

2,

3} , P. Ballone ₄

Affiliation

系统的分子动力学模拟基于经验力场已经进行了用于三乙基三氟甲磺酸酯的样品（三乙三氟甲磺酸酯，[TEA] [TF]），覆盖一个宽的温度范围为200K≤ Ť ≤400 K和分析了广泛的一组属性从自扩散和电导率到旋转弛豫和氢键动力学。这项研究是由最近准弹性中子散射和在同一系统上差示扫描量热法测量的动机，揭示在两个连续的一阶转变Ť ≈230和310 K（加热），以及一个有趣的和部分不明原因的各种subdiffusive的酸性质子的运动。仿真显示在T处有一个弱的不连续过渡= 310 K，并突出显示了离子的旋转弛豫中T = 260 K处的异常，这是我们在T = 230 K处的实验跃迁的模拟模拟中识别出的。因此，模拟有助于识别实验跃迁的性质，从而确认了最高温度之一对应于熔化，而在较低的一个正在发生Ť是从晶体的过渡，稳定在Ť ≤260 K，在塑料相（260≤ Ť ≤310 K），其中分子能够旋转而不扩散。尤其是旋转导致了中间T处的亚扩散运动无论是在实验中还是在仿真中。通过分子动力学和密度泛函计算研究了氢键的结构，分布和强度。还讨论了具有相同符号的离子的聚集以及水在1％wgt浓度下被水污染的影响。

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Density Functional Computations and Molecular Dynamics Simulations of the Triethylammonium Triflate Protic Ionic Liquid

Systematic molecular dynamics simulations based on an empirical force field have been carried out for samples of triethylammonium trifluoromethanesulfonate (triethylammonium triflate, [TEA][Tf]), covering a wide temperature range 200 K ≤ T ≤ 400 K and analyzing a broad set of properties, from self-diffusion and electrical conductivity to rotational relaxation and hydrogen-bond dynamics. The study is motivated by recent quasi-elastic neutron scattering and differential scanning calorimetry measurements on the same system, revealing two successive first order transitions at T ≈ 230 and 310 K (on heating), as well as an intriguing and partly unexplained variety of subdiffusive motions of the acidic proton. Simulations show a weakly discontinuous transition at T = 310 K and highlight an anomaly at T = 260 K in the rotational relaxation of ions that we identify with the simulation analogue of the experimental transition at T = 230 K. Thus, simulations help identifying the nature of the experimental transitions, confirming that the highest temperature one corresponds to melting, while the one taking place at lower T is a transition from the crystal, stable at T ≤ 260 K, to a plastic phase (260 ≤ T ≤ 310 K), in which molecules are able to rotate without diffusing. Rotations, in particular, account for the subdiffusive motion seen at intermediate T both in the experiments and in the simulation. The structure, distribution, and strength of hydrogen bonds are investigated by molecular dynamics and by density functional computations. Clustering of ions of the same sign and the effect of contamination by water at 1% wgt concentration are discussed as well.

更新日期：2017-12-11

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