Molecular dynamics simulation of complex molecules using quantum-chemical potentials: application to modelling fuel droplets

提出了一种新的用于模拟复杂碳氢化合物分子的混合量子力学/分子动力学(QM/MD)模型，并将该模型应用于柴油机模拟条件下正十二烷、正十二烷和二丙基苯分子混合物的模拟。通过求解与时间无关的薛定谔方程，我们可以得到一个分子或分子系综的平衡几何结构，并计算出原子和电子在体系中任何位置的势能。这个方法将给出分子相互作用的势能，它是分子几何结构的函数。将单个C和H原子和分子相互作用的能量与传统MD方法计算的相互作用能进行比较(考虑到分子的内部自由度，在我们目前的EPSRC项目EP/H001603/1中使用)，将使我们能够分析QM势和经典势的差异。预计我们的结果将被用来计算经典MD计算中使用的势的修正。新的混合模型将利用EPSRC项目EP/H001603/1期间开发的技术，用于分析正十二烷在液、气相和液/气界面的动力学。预计在这个阶段，我们将能够确定传统MD方法的适用范围。将发展一种新的近似方法，考虑对经典结果的QM修正。此外，考虑到动态区中存在两种成分(燃料蒸气和空气)的先前开发的动力学模型将被推广，以考虑那里存在三种成分(两种燃料和一种空气)。这些新模型将应用于实际发动机条件下柴油液滴加热和蒸发的分析。与以前建立的模型不同，该模型除了考虑液滴内部温度梯度和回流的影响外，还考虑了蒸发过程中边界移动的影响。这将是一个合作项目，来访的研究员Vladimir M.Gun‘ko教授(乌克兰基辅乌克兰国家科学院Chuiko表面化学研究所)是国际公认的界面现象专家；曹炳洋博士(清华大学，北京，P.R.中国)，他的专长包括开发分子动力学模拟数值算法；Irina Shishkova博士(俄罗斯莫斯科动力工程研究所)，其专业知识集中在解Boltzmann方程的数值代码的开发上。它将由Sergei Sazhin教授领导，他的专业知识包括开发燃料液滴加热和蒸发的新物理模型，以期应用于内燃机过程的建模。合作研究员Morgan Heikal教授将就模型与汽车应用的相关性向项目成员提供建议。该项目还将包括一名研究员。该项目将建立在目前获得资助的EPSRC项目EP/H001603/1的基础上，支持私营部门、B-Y博士之间的合作。此外，还支持国际和平研究所和I.Shishkova博士之间的合作，以及以前资助的EPSRC项目EP/C527089/1和EP/E02243X/1，以及皇家学会与俄罗斯的联合项目，支持国际和平协会和I.Shishkova博士之间的合作。

This proposal is concerned with the development of a new hybrid quantum mechanics/ molecular dynamics (QM/MD) model for the simulation of complex hydrocarbon molecules and the application of this model to the simulation of n-dodecane and a mixture of n-dodecane and dipropylbenzene molecules in Diesel engine-like conditions. The solution of the time independent Schrodinger equation will allow us to obtain the equilibrium geometry of a molecule or an ensemble of molecules, and to calculate the potential energy for any position of atoms and electrons in the system. This approach will give us the potential energy of interacting molecules as a function of their geometry. Comparison of this energy for interacting individual C and H atoms and molecules with the interaction energy calculated by the conventional MD approach (taking into account the internal degrees of freedom of molecules, used in our current EPSRC project EP/H001603/1) for the same inter-atomic distances will allow us to analyse the differences in the QM and classical potentials. It is anticipated that our results will be used to calculate the corrections for the potentials used in the classical MD calculations. The new hybrid model will be used for the analysis of the dynamics of n-dodecane molecules in liquid and gas phases and at the liquid/gas interface, using techniques developed during the work on EPSRC project EP/H001603/1. It is anticipated that at this stage we will be able to establish the range of applicability of the conventional MD approach. A new approximate method of taking into account the QM corrections to the classical results will be developed. Also, the previously developed kinetic model, taking into account the presence of two components (fuel vapour and air) in the kinetic region will be generalised to take into account the presence of the three components (two species of fuel and one of air) there. These new models will be applied to the analysis of Diesel fuel droplet heating and evaporation in realistic engine conditions. In contrast to the previously developed models, the kinetic effects will be taken into account alongside the effects of temperature gradient and recirculation inside droplets and the effects of the moving boundary during the evaporation process. We are not aware of any previous research in this area.This will be a collaborative project involving visiting researchers Professor Vladimir M. Gun'ko (Chuiko Institute of Surface Chemistry of the National Academy of Sciences of Ukraine, Kiev, Ukraine) who is an internationally recognised expert in interfacial phenomena, Dr Bing-Yang Cao (Tsinghua University, Beijing, P.R. China), whose expertise includes the development of numerical algorithms for molecular dynamics simulation and Dr Irina Shishkova (Moscow Power Engineering Institute, Russia), whose expertise is focused on the development of numerical codes for the solution of the Boltzmann equation. It will be led by Professor Sergei Sazhin, whose expertise includes the development of new physical models of fuel droplet heating and evaporation with a view of applications to modelling the processes in internal combustion engines. The Co-investigator Professor Morgan Heikal will advise the project members on the relevance of the models to automotive applications. A Research Fellow will also be included in the project. This project will build upon the currently funded EPSRC project EP/H001603/1, supporting the collaboration between the PI, Dr B-Y. Cao and Dr I. Shishkova, and previously funded EPSRC projects EP/C527089/1 and EP/E02243X/1, and a Royal Society Joint project with Russia, supporting the collaboration between the PI and Dr I. Shishkova.