Embedded Cluster Modelling for Realistic Solid-State Systems

现代高度并行计算(HPC)基础设施的出现，加上可扩展软件包的开发，导致了材料化学建模应用的前所未有的增长--现在，如果不包括模拟来理解观测或预测新颖性，进行高影响的研究是不可想象的。在材料化学模型界，最广泛使用的技术是周期密度泛函理论(DFT)。这种方法对于具有高度对称性的体系(即单位晶胞中的原子很少)是非常有效的；然而，当扩展模型以解决诸如紧密堆积的离子材料上的表面反应性等问题时，存在着一个重大挑战。典型的解决办法是创建一个重复的表面模型(即表面超单元)，该模型在表面范数中足够大，并跨越真空区，以确保消除虚假的“图像”相互作用，并包含几层“不活跃”的亚表面原子，以确保化学有效性。虽然实用，但这种方法正在节流计算模拟对应用催化化学的影响，因为增加的模型尺寸导致计算开销，将计算精度限制在较低的DFT水平。因此，需要实现新的方法来实现更高精度、更逼真的固态系统模拟。在这项工作中，我的目标是扩展嵌入簇混合量子力学/分子力学(QM/MM)方法，以挑战工作规范，并提供一个可行的选择来取代周期DFT。嵌入团簇方法去除了周期性边界条件，QM/MM方法允许将感兴趣的电子空间缩小到活性中心周围的原子，从而在不影响化学精度的情况下降低了计算成本。为了实现这一目标，需要进行大量的开发工作，以使这项技术可用于表面反应的固态建模，包括简化设置程序(集群设计、力场参数化)。此外，我建议扩展QM/MM以精确地模拟磁性材料：通过开发新的赝势和波函数嵌入方法，将合适的势施加到QM/MM边界的QM原子上，从而实现精确的嵌入环境。开发成果将通过与工业相关的绿色催化过程的研究来验证，这些过程使用金属氧化物，我们最高级别的基准是阳离子掺杂氧化铁晶型催化的量子化学模拟。这些研究将扩展到以前无法触及的材料模拟领域，例如阐明含锰和含铁钙钛矿对析氧反应的反应性，以及模拟当代2D磁性材料的缺陷性质和反应性。通过联谊会的成果，将为扩展系统实现准确、高水平的DFT和后Hartree Fock方法，它们的应用将使人们能够前所未有地深入了解紧急材料的化学性质，并开辟出一系列超越固态的更令人兴奋的科学领域。

The advent of modern highly-parallelised computing (HPC) infrastructure, coupled with development of scalable software packages, has led to unprecedented growth in the application of materials chemistry modelling - it is now unthinkable to perform high-impact research without including simulations to either understand observations or predict novelty. Within the materials chemistry modelling community, the most widely-used technique is periodic density functional theory (DFT). Such an approach is highly efficient for systems with high-symmetry (i.e. few atoms in the unit cell); however, a major challenge exists when expanding the model to tackle problems such as surface reactivity on close-packed ionic materials. The typical workaround is to create a repeating surface model (i.e. a surface supercell), which is big enough in the surface norm and across the vacuum region to ensure the removal of spurious "image" interactions, and has several layers of "inactive" sub-surface atoms included to ensure chemical validity. Whilst pragmatic, this approach is throttling the impact of computational simulation on applied catalytic chemistry, because the increased model size results in computational overheads that limit computational accuracy to the lower levels of DFT. Therefore, new approaches need to be realised that enable higher accuracy, realistic simulation for solid-state systems.In this work, my aim is to extend the embedded-cluster hybrid quantum-/molecular-mechanics (QM/MM) approach in order to challenge the working norm and offer a viable option instead of periodic-DFT. The embedded-cluster approach removes periodic boundary conditions, and QM/MM can allow the reduction of the electronic space of interest to just the atoms around an active site, thus reducing computational cost without compromising chemical accuracy. To achieve this goal, significant development work is needed to make this technique accessible for solid-state modelling of surface reactions, including streamlining of the setup procedures (cluster design, forcefield parameterisation). Additionally, I propose extensions of QM/MM to accurately model magnetic materials: accurate embedding environments, which apply appropriate potentials to QM atoms at the QM/MM boundary, will be realised through development of novel pseudopotentials and wavefunction embedding approaches. The development outcomes will be validated by investigations of industrially-relevant green catalytic processes for H2 synthesis, which use metal oxides, with our highest-level benchmark being quantum chemical simulations of catalysis on cation-doped iron oxide polymorphs. These investigations will be followed with extension into previously inaccessible fields of materials simulation, such as elucidating reactivity of Mn- and Fe- containing perovskites for the oxygen evolution reaction, and simulating defect properties and reactivity for contemporary 2D magnetic materials. Accurate, high-level DFT and post-Hartree Fock approaches will be realised for extended systems through the Fellowship outcomes, and their application will allow unprecedented insight into chemical properties of emergent materials, as well as opening up a range of further exciting scientific areas beyond the solid-state.