arXivDaily arXiv每日学术速递 周一至周五更新
北美退伍军人节(Veterans Day),12 日无更新
arXiv 0811.0272cond-mat.soft
收藏

液态甲醇的多时间尺度行为和网络动力学

Multiple Time-Scale Behaviour and Network Dynamics in Liquid Methanol

Ruchi Sharma, Charusita Chakravarty

摘要:

正则系综分子动力学模拟的液体甲醇,建模使用刚体,对添加剂的潜力,被用来计算静态分布和时间相关的标记分子的势能作为一种手段,表征液态动力学。标记的分子势能的静态分布显示出一个明确的多峰结构,具有三个不同的峰,类似于先前在水和液体二氧化硅中观察到的。的多模态示出源自静电效应,但不是从本地,氢键相互作用。这项研究的一个有趣的结果是甲醇,水和二氧化硅的标记的势能功率谱显着的相似性,尽管在底层的相互作用和网络的维数的差异。所有这三种液体显示出一个独特的多时间尺度(MTS)制度与1/f的依赖性与标度指数α和扩散率之间的明确的正相关性。MTS范围的低频极限由在标准温度和压力条件下甲醇情况下发生在约0.1 cm{-1}处的白噪声行为的交叉频率确定。在所有三个系统中,200 cm{-1}以上的功率谱区主要由局部振动引起的共振(如天平动)所支配。$α$和在所有三种液体中的扩散率之间的相关性似乎与局部运动和较大长度/时间尺度网络重组之间的耦合强度有关。因此,与网络重组动力学的时间尺度似乎是定性相似的,在这些系统中,尽管水和二氧化硅都显示扩散异常,但甲醇没有。

英文摘要:

Canonical ensemble molecular dynamics simulations of liquid methanol, modeled using a rigid-body, pair-additive potential, are used to compute static distributions and temporal correlations of tagged molecule potential energies as a means of characterising the liquid state dynamics. The static distribution of tagged molecule potential energies shows a clear multimodal structure with three distinct peaks, similar to those observed previously in water and liquid silica. The multimodality is shown to originate from electrostatic effects, but not from local, hydrogen-bond interactions. An interesting outcome of this study is the remarkable similarity in the tagged potential energy power spectra of methanol, water and silica, despite the differences in the underlying interactions and the dimensionality of the network. All three liquids show a distinct multiple time scale (MTS) regime with a 1/f dependence with a clear positive correlation between the scaling exponent alpha and the diffusivity. The low-frequency limit of the MTS regime is determined by the frequency of crossover to white noise behaviour which occurs at approximately 0.1 cm{-1} in the case of methanol under standard temperature and pressure conditions. The power spectral regime above 200 cm{-1} in all three systems is dominated by resonances due to localised vibrations, such as librations. The correlation between $α$ and the diffusivity in all three liquids appears to be related to the strength of the coupling between the localised motions and the larger length/time-scale network reorganizations. Thus the time scales associated with network reorganization dynamics appear to be qualitatively similar in these systems, despite the fact that water and silica both display diffusional anomalies but methanol does not.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑