Ojwang J G O, van Santen Rutger, Kramer Gert Jan, van Duin Adri C T, Goddard William A
Schuit Institute of Catalysis, Eindhoven University of Technology, Postbus 513, 5600 MB, Den Dolech 2, Eindhoven, The Netherlands.
J Chem Phys. 2008 Apr 28;128(16):164714. doi: 10.1063/1.2908737.
We have parametrized a reactive force field for NaH, ReaxFF(NaH), against a training set of ab initio derived data. To ascertain that ReaxFF(NaH) is properly parametrized, a comparison between ab initio heats of formation of small representative NaH clusters with ReaxFF(NaH) was done. The results and trend of ReaxFF(NaH) are found to be consistent with ab initio values. Further validation includes comparing the equations of state of condensed phases of Na and NaH as calculated from ab initio and ReaxFF(NaH). There is a good match between the two results, showing that ReaxFF(NaH) is correctly parametrized by the ab initio training set. ReaxFF(NaH) has been used to study the dynamics of hydrogen desorption in NaH particles. We find that ReaxFF(NaH) properly describes the surface molecular hydrogen charge transfer during the abstraction process. Results on heat of desorption versus cluster size shows that there is a strong dependence on the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. To gain more insight into the structural transformations of NaH during thermal decomposition, we performed a heating run in a molecular dynamics simulation. These runs exhibit a series of drops in potential energy, associated with cluster fragmentation and desorption of molecular hydrogen. This is consistent with experimental evidence that NaH dissociates at its melting point into smaller fragments.
我们针对NaH构建了一个反应力场ReaxFF(NaH)，并以一组从头算得出的数据作为训练集。为确定ReaxFF(NaH)的参数设置是否恰当，我们对具有代表性的小NaH团簇的从头算生成热与ReaxFF(NaH)进行了比较。结果发现，ReaxFF(NaH)的结果和趋势与从头算值一致。进一步的验证包括比较从从头算和ReaxFF(NaH)计算得出的Na和NaH凝聚相的状态方程。两者结果匹配良好，表明ReaxFF(NaH)通过从头算训练集进行了正确的参数设置。ReaxFF(NaH)已被用于研究NaH颗粒中氢解吸的动力学。我们发现ReaxFF(NaH)能够恰当地描述提取过程中表面分子氢的电荷转移。解吸热与团簇尺寸的结果表明，解吸热对颗粒尺寸有很强的依赖性，这意味着纳米结构化增强了解吸过程。为了更深入了解NaH在热分解过程中的结构转变，我们在分子动力学模拟中进行了加热运行。这些运行显示出一系列势能下降，与团簇破碎和分子氢解吸有关。这与NaH在熔点分解为较小碎片的实验证据一致。
