Kritikos Efstratios M, Lele Aditya, van Duin Adri C T, Giusti Andrea
Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, United Kingdom.
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA.
J Chem Phys. 2023 Feb 7;158(5):054109. doi: 10.1063/5.0134785.
Reactive Molecular Dynamics (MD) and Density Functional Theory (DFT) computations are performed to provide insight into the effects of external electrostatic fields on hydrocarbon reaction kinetics. By comparing the results from MD and DFT, the suitability of the MD method in modeling electrodynamics is first assessed. Results show that the electric field-induced polarization predicted by the MD charge equilibration method is in good agreement with various DFT charge partitioning schemes. Then, the effects of oriented external electric fields on the transition pathways of non-redox reactions are investigated. Results on the minimum energy path suggest that electric fields can cause catalysis or inhibition of oxidation reactions, whereas pyrolysis reactions are not affected due to the weaker electronegativity of the hydrogen and carbon atoms. MD simulations of isolated reactions show that the reaction kinetics is also affected by applied external Lorentz forces and interatomic Coulomb forces since they can increase or decrease the energy of collision depending on the molecular conformation. In addition, electric fields can affect the kinetics of polar species and force them to align in the direction of field lines. These effects are attributed to energy transfer via intermolecular collisions and stabilization under the external Lorentz force. The kinetics of apolar species is not significantly affected mainly due to the weak induced dipole moment even under strong electric fields. The dynamics and reaction rates of species are studied by means of large-scale combustion simulations of n-dodecane and oxygen mixtures. Results show that under strong electric fields, the fuel, oxidizer, and most product molecules experience translational and rotational acceleration mainly due to close charge transfer along with a reduction in their vibrational energy due to stabilization. This study will serve as a basis to improve the current methods used in MD and to develop novel methodologies for the modeling of macroscale reacting flows under external electrostatic fields.
进行了反应分子动力学（MD）和密度泛函理论（DFT）计算，以深入了解外部静电场对烃类反应动力学的影响。通过比较MD和DFT的结果，首先评估了MD方法在模拟电动力学方面的适用性。结果表明，MD电荷平衡方法预测的电场诱导极化与各种DFT电荷划分方案高度一致。然后，研究了定向外部电场对非氧化还原反应过渡途径的影响。关于最小能量路径的结果表明，电场可以导致氧化反应的催化或抑制，而热解反应由于氢和碳原子的电负性较弱而不受影响。孤立反应的MD模拟表明，反应动力学也受到施加的外部洛伦兹力和原子间库仑力的影响，因为它们可以根据分子构象增加或降低碰撞能量。此外，电场可以影响极性物种的动力学，并迫使它们沿场线方向排列。这些影响归因于通过分子间碰撞的能量转移和外部洛伦兹力作用下的稳定化。非极性物种的动力学主要由于即使在强电场下诱导偶极矩也较弱而没有受到显著影响。通过对正十二烷和氧气混合物的大规模燃烧模拟研究了物种的动力学和反应速率。结果表明，在强电场下，燃料、氧化剂和大多数产物分子主要由于紧密的电荷转移而经历平动和转动加速，同时由于稳定化其振动能量降低。这项研究将为改进当前MD中使用的方法以及开发用于模拟外部静电场下宏观尺度反应流的新方法奠定基础。
