Moqadam Mahmoud, Riccardi Enrico, Trinh Thuat T, Åstrand Per-Olof, van Erp Titus S
Department of Chemistry, Norwegian University of Science and Technology (NTNU), Høgskoleringen 5, Realfagbygget D3-117, 7491 Trondheim, Norway.
J Chem Phys. 2015 Nov 14;143(18):184113. doi: 10.1063/1.4935179.
We studied silica dimerization reactions in the gas and aqueous phase by density functional theory (DFT) and reactive force fields based on two parameterizations of ReaxFF. For each method (both ReaxFF force fields and DFT), we performed constrained geometry optimizations, which were subsequently evaluated in single point energy calculations using the other two methods. Standard fitting procedures typically compare the force field energies and geometries with those from quantum mechanical data after a geometry optimization. The initial configurations for the force field optimization are usually the minimum energy structures of the ab initio database. Hence, the ab initio method dictates which structures are being examined and force field parameters are being adjusted in order to minimize the differences with the ab initio data. As a result, this approach will not exclude the possibility that the force field predicts stable geometries or low transition states which are realistically very high in energy and, therefore, never considered by the ab initio method. Our analysis reveals the existence of such unphysical geometries even at unreactive conditions where the distance between the reactants is large. To test the effect of these discrepancies, we launched molecular dynamics simulations using DFT and ReaxFF and observed spurious reactions for both ReaxFF force fields. Our results suggest that the standard procedures for parameter fitting need to be improved by a mutual comparative method.
我们通过基于ReaxFF两种参数化的密度泛函理论（DFT）和反应力场研究了气相和水相中二氧化硅的二聚反应。对于每种方法（ReaxFF力场和DFT），我们都进行了受限几何优化，随后使用其他两种方法在单点能量计算中对其进行评估。标准的拟合程序通常在几何优化后将力场能量和几何结构与量子力学数据的能量和几何结构进行比较。力场优化的初始构型通常是从头算数据库的最低能量结构。因此，从头算方法决定了正在研究哪些结构以及正在调整力场参数，以便最小化与从头算数据的差异。结果，这种方法不会排除力场预测出实际上能量非常高、因此从头算方法从未考虑过的稳定几何结构或低过渡态的可能性。我们的分析表明，即使在反应物之间距离较大的非反应条件下，也存在这种非物理几何结构。为了测试这些差异的影响，我们使用DFT和ReaxFF进行了分子动力学模拟，并观察到两种ReaxFF力场都出现了虚假反应。我们的结果表明，需要通过相互比较的方法改进参数拟合的标准程序。
