Reactive molecular dynamics (MD) simulations, especially those employing acceleration techniques, can provide useful insights on the mechanism underlying the transformation of buried organic matter, yet, so far, it remains extremely difficult to predict the time scales associated with these processes at moderate temperatures (i.e., when such time scales are considerably larger than those accessible to MD). We propose here an accelerated method based on flux sampling and kinetic integration along a 1D order parameter that can considerably extend the accessible time scales. We demonstrate the utility of this technique in an application to the dehydration of crystalline cellulose at temperatures ranging from 1900 K to 1500 K. The full decomposition is obtained at all temperatures apart from T = 1500 K, showing the same distribution of the main volatiles (H2O, CO, and CO2) as recently obtained using replica exchange molecular dynamics. The kinetics of the process is well fitted with an Arrhenius law with Ea = 93 kcal/mol and k0 = 9 × 1019 s-1, which are somehow larger than experimental reports. Unexpectedly, the process seems to considerably slow down at lower temperatures, severely departing from the Arrhenius regime, probably because of an inadequate choice of the order parameter. Nevertheless, we show that the proposed method allows considerable time sampling at low temperatures compared to conventional MD.

中文翻译：

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使用通量采样分子动力学和一维动力学积分预测复杂多壁垒路径的时标：在纤维素脱水中的应用。

反应性分子动力学（MD）模拟，尤其是那些采用加速技术的模拟，可以提供有关埋藏有机物转化的潜在机制的有用见解，然而，到目前为止，在中等温度下预测与这些过程相关的时间尺度仍然极为困难（即，这种时标比MD可以访问的时标大得多）。我们在此提出一种基于通量采样和沿一维参数的动力学积分的加速方法，该方法可以大大扩展可访问的时间尺度。我们证明了该技术在1900 K至1500 K温度范围内结晶纤维素脱水中的应用。在除T = 1500 K以外的所有温度下均可完全分解，显示出与最近使用仿制交换分子动力学获得的主要挥发物（H2O，CO和CO2）相同的分布。该过程的动力学非常符合Arrhenius律，Ea = 93 kcal / mol，k0 = 9×1019 s-1，比实验报道要大。出乎意料的是，该过程似乎在较低温度下会大大减慢速度，从而严重偏离了Arrhenius体制，这可能是由于订购参数选择不充分所致。尽管如此，我们表明，与传统的MD相比，该方法在低温下可进行大量的时间采样。比实验报告要大一些。出乎意料的是，该过程似乎在较低温度下会大大减慢速度，从而严重偏离了Arrhenius体制，这可能是由于订购参数选择不充分所致。尽管如此，我们表明，与传统的MD相比，该方法在低温下可进行大量的时间采样。比实验报告要大一些。出乎意料的是，该过程似乎在较低温度下会大大减慢速度，从而严重偏离了Arrhenius体制，这可能是由于订购参数选择不充分所致。尽管如此，我们表明，与传统的MD相比，该方法在低温下可进行大量的时间采样。