几种新型含能材料中相互作用与物性的理论研究

发布时间：2018-05-11 18:02

本文选题：含能材料 + 分子晶体　；参考：《大连理工大学》2015年博士论文

【摘要】：含能材料(EMs),包括炸药、推进剂和烟火剂等,已广泛应用于国民经济和国防工业等各个领域。因此,含能材料的基础研究对国民经济的增长和国防工业的发展都有着重要的意义。由于含能材料的实验研究具有一定的危险性,计算机模拟逐渐成为含能材料研究的重要手段之一。本文基于密度泛函理论,并结合分子动力学模拟,分别研究了分子晶体中分子间相互作用,金属有机物骨架聚合物含能材料的晶体结构、电子结构和弹性性质,以及新型钝感炸药FOX-7晶体在常压和高压下的热解行为。目前,大部分含能材料属于分子晶体,分子晶体中分子间的相互作用决定了其晶体结构及其物理化学性质描述的准确性。然而,基于局域密度近似或者广义梯度近似的密度泛函理论由于不能描述长程关联相互作用,不能很好地描述分子晶体中的相互作用。为了能更好地描述分子间相互作用,人们已经发展了多种方案来弥补密度泛函理论框架下这些近似的缺陷。虽然人们对分子二聚体、分子团簇等体系进行了大量的测试,但是这些修正方案在描述分子晶体的表现却知之甚少。本文系统地测试了密度泛函理论及其修正方案在描述分子晶体中相互作用时的表现,为分子晶体的物理化学性质及其动力学性质的研究提供可靠的方法指导。我们首先对甲烷晶体的结构进行了测试,发现通过加入经验对势来修正DFT的PBE-Grimme(PBE-D2)和PBE-D3方案可以很好地重复实验的晶格常数和晶格能,而且和标准DFT计算相比计算成本增加不明显；而vdW-DF方案尽管可以给出合理的晶格常数和体弹性模量,但却高估了甲烷晶体的晶格能,并且增加了计算成本。更进一步,我们采用合作者针对包含C、H、N和O体系发展了DFT+LAP方案,计算了十二种分子晶体的晶格常数和晶格能。通过和实验值及PBE-Grimme的计算结果相对比,评估了此方案在描述分子间相互作用时的表现。结果表明,我们合作者发展的DFT+LAP得到的计算结果与实验值相符合,而且计算量也与DFT方案基本相当；另一方面,PBE-Grimme方案是测试的所有方案中最好的,我们的计算结果与之相近。因此,DFT+LAP方案在研究分子晶体和其它非共价键相互作用体系时是一种高效且精确的计算方法。随后,我们更进一步改进和发展了DFT+LAP方法,研究指出需要更有效的势函数才可以更精确描述分子晶体中分子间的相互作用。和传统炸药相比,人们己经合成出了高含氮量且具有更优异的爆轰性能的金属有机骨架聚合物(MOF),这类材料被证实为潜在的新型含能材料。金属有机骨架聚合物的晶体结构极其复杂,其电子结构和力学性质对这类潜在含能材料的应用有着重要的影响。本文采用第一性原理方法系统地研究了一维、二维和三维MOF-EMs的晶体结构、电子结构和弹性性质。我们首先对MOF-EMs的晶体结构用PBE泛函及色散修正方案进行测试。结果表明,PBE泛函明显地低估了MOF-EMs晶体中的非共价键相互作用,从而高估了晶格常数。所有的修正方法都或多或少地修正了对分子晶体晶格常数的描述,但是一些方案如PBE-D和optB88-vdW却过度修正这种效应。在所有方案中,optPBE-vdW可以获得与实验最一致的晶体结构。电子结构分析表明只有NHN为金属,其余MOF-EMs为半导体或绝缘体。我们进一步讨论了MOF-EMs的电子结构和其感度之间的关系,指出相似结构的带隙越大,MOF的冲击感度越高,则MOF越不敏感,这和实验相符。此外,我们预测的MOF-EMs的体弹性模量介于15.1-35.0 GPa之间,高于传统炸药的体弹性模量。除了含能材料的基本性质,其爆轰机制的研究也是含能材料的研究热点。FOX-7作为一种新型钝感炸药,理解其热解机制不仅对FOX-7的储藏、运输和应用都有着重要的意义,还有助于新型钝感炸药的设计。本文采用第一性原理分子动力学模拟研究了FOX-7晶体在常压和高压下的热解过程。常压热解过程表明FOX-7的起始分解从C—NO2键的断裂开始。我们详细地分析了热解产物及其演化规律。结果表明热解产物包含大量的N2、H2O,还包含少量的CO、CO2等。同时发现中间产物NO、NO2、OH等分子片段都携带电荷,这些带电分子片段可能会促进FOX-7的后续化学反应。进一步模拟压力对热解的影响指出压力的增加并不直接对热解机制产生影响,却加快了热解反应发生的速率。
[Abstract]:The energetic materials (EMs), including explosives, propellants and pyrotechnics, have been widely used in various fields such as national economy and national defense industry. Therefore, the basic research of energetic materials is of great significance to the growth of national economy and the development of national defense industry. In this paper, based on the density functional theory and molecular dynamics simulation, this paper studies the intermolecular interaction in molecular crystals, the crystal structure, the electronic structure and the elastic properties of the energetic materials, as well as the new insensitive explosive FOX-7 crystal at normal pressure. At present, most of the energetic materials are molecular crystals, and the intermolecular interactions in molecular crystals determine the accuracy of their crystal structure and the description of their physical and chemical properties. However, the density functional theory based on local density approximation or generalized gradient approximation can not describe the interaction of long range correlation, The interaction in molecular crystals can not be well described. In order to better describe intermolecular interactions, a variety of schemes have been developed to compensate for these approximate defects in the framework of density functional theory. Although a large number of systems have been tested for molecular two polymer, molecular clusters and other systems, these modifications are described The expression of molecular crystal is little known. This paper systematically tests the performance of density functional theory and its modified scheme in describing the interaction of molecular crystals. It provides a reliable method for the study of the physicochemical properties and kinetic properties of molecular crystals. First, we have tested the structure of methane crystal and found that the structure of the crystal is tested. The lattice constant and lattice energy of the DFT PBE-Grimme (PBE-D2) and PBE-D3 schemes can be well repeated by adding the experience to the potential, and the increase of the computational cost is not obvious compared with the standard DFT calculation. While the vdW-DF scheme can give reasonable lattice constants and bulk modulus of elasticity, but it overestimates the lattice energy of the methane crystal. In addition, we used the collaborators to develop the DFT+LAP scheme for the C, H, N and O systems. We calculated the lattice constants and lattice energies of the twelve molecular crystals. By comparing the experimental values and the calculated results of PBE-Grimme, we evaluated the performance of this case in describing intermolecular interactions. It is clear that the calculated results obtained by our collaborators are in accordance with the experimental values, and the amount of calculation is similar to that of the DFT scheme; on the other hand, the PBE-Grimme scheme is the best of all the solutions of the test, and our calculation results are similar. Therefore, the DFT+LAP scheme is studying the interaction between the molecular crystal and other non covalent bonds. The system is an efficient and accurate method of calculation. Then, we have further improved and developed the DFT+LAP method. It is pointed out that more effective potential functions are needed to describe the intermolecular interactions in molecular crystals more accurately. Compared with traditional explosives, people have synthesized high nitrogen content and have better detonation properties. The metal organic skeleton polymer (MOF) can be proved to be a potential new energetic material. The crystal structure of the metal organic framework polymer is extremely complex. Its electronic structure and mechanical properties have an important influence on the application of this kind of potential energetic material. This paper systematically studies one dimension and two dimension by the first principle method. The crystal structure, the electronic structure and the elastic properties of the three-dimensional MOF-EMs. We first test the crystal structure of MOF-EMs by PBE functional and dispersion correction scheme. The results show that the PBE functional significantly underestimates the non covalent bond interaction in the MOF-EMs crystal and overestimates the lattice constant. All the correction methods are more or less repaired. The crystal lattice constants of molecular crystals are described, but some schemes, such as PBE-D and optB88-vdW, have overcorrected this effect. In all schemes, optPBE-vdW can obtain the most consistent crystal structure with the experiment. The electronic structure analysis shows that only NHN is metal and the rest MOF-EMs is half conductor or insulator. We further discuss the MOF-EMs The relationship between the electronic structure and its sensitivity indicates that the larger the band gap of the similar structure is, the higher the impact sensitivity of MOF is, the less sensitive the MOF is, which is in agreement with the experiment. In addition, the bulk modulus of the predicted MOF-EMs is between the 15.1-35.0 GPa and the bulk modulus of the traditional explosive. The research is also a hot spot of energy containing materials.FOX-7 as a new type of insensitive explosive. Understanding its pyrolysis mechanism is not only important for the storage, transportation and application of FOX-7, but also for the design of new insensitive explosives. In this paper, the heat of FOX-7 crystal under normal pressure and high pressure is studied by the first principle molecular dynamics model. The pyrolysis process at the normal pressure indicates that the initial decomposition of the FOX-7 begins with the fracture of the C NO2 bond. We have analyzed the pyrolysis products and their evolution rules in detail. The results show that the pyrolysis products contain a large number of N2, H2O, and a small amount of CO, CO2, etc., and that the intermediate products NO, NO2, OH, etc. carry charge, these charged molecules The section may promote the subsequent chemical reaction of FOX-7. Further simulation of the effect of pressure on pyrolysis indicates that the increase of pressure does not directly affect the pyrolysis mechanism, but accelerates the rate of the pyrolysis reaction.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB34

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