Computational methods for the exploration of potential energy surfaces with applications to nanoalloy materials.

我们开发了高性能的计算方法来探索势能面（PES，描述分子几何形状变化时分子能量变化的数学函数），从而为分子结构和化学反应性的研究提供了基础。这一提议的成功实施将创造一套独特的计算工具，用于研究分子结构、过渡态和反应路径，以及具有数百个原子的系统的模拟。这些工具对加拿大和其他国家的研究人员都非常重要。我们的一种方法模拟了DFT，并给出了4到6个数量级的计算加速。它将允许纳米合金*在催化和数据存储设备方面的潜在应用研究。根据我们最近发现的双金属笼子的线索，我们将寻找新的更大的全金属笼子。** PES的最小值是分子的平衡几何形状；鞍点是过渡状态；连接鞍点和最小值的最陡下降线为反应路径；最陡下降线附近的低能区对于反应机制的详细模型是重要的。我们将继续利用量子化学和密度泛函理论（DFT），结合我们自己的计算机代码来研究PES。**学生将在结合方法开发*和应用程序的研究项目中接受培训，并将获得各种技能：UNIX*和量子化学软件的专业知识，编程和shell脚本，数学建模和一般科学素养。这些项目在不同层次上设计，以满足本科生、研究生和博士后的需求和能力。我们将从三个方面研究纳米合金，这些纳米合金在催化和信息技术方面具有有趣的特性和潜在的用途。**(1)全局优化。进化计算方法，如遗传算法（GA），将被用来确定纳米合金簇的几何结构。**(2)反应机理。我们已经使用粒子群优化（PSO）来发现，在没有人类监督的情况下，在化学反应（“反应机制”）中发生的分子几何变换序列。我们将创造一种基于化学直觉和优化技术的新方法，来寻找先验的（不需要任何DFT计算）反应机理。我们将在个案的基础上发现，这种机制是否很好地近似于最低能量的反应路径（真正的机制），并将相应地对化学反应进行分类。**(3)原子模拟。我们开发了一种新的拟合方法，用于创建高维PES，它是全自动的，不需要用户输入函数形式，并且几乎适用于任何化学成分。这个PES函数模拟了一种精确的方法（DFT），并提供了相对于DFT的4到6个数量级的加速。我们将使用它来进行精确的蒙特卡罗（AIMC）模拟，其中PES与“重要性采样”一起使用，以提供极大的计算速度。我们还将采用双管齐下的方法*进行全局优化，其中我们使用PES函数筛选*大量几何结构并生成一个更小的子集*，用于计算DFT能量。在这三个方面的工作，我们将试图揭示控制相对稳定性和几何结构的原理，以及双金属团簇的磁性、电子和化学性质。基于这些原理和我们团队独有的新方法，我们将设计稳定的纳米合金，用于催化和磁性数据存储设备。

We develop high performance computational methods to explore potential*energy surfaces (PES, mathematical functions that describe how the energy of*molecules changes when the geometry of the molecule changes), thus providing the*foundation for studies of molecular structure and chemical reactivity. Successful implementation*of this proposal will create a unique set of computational tools for studying*molecular structures, transition states, and reaction paths,*and for the simulation of systems with hundreds of atoms. These tools*will be of great importance to researchers in Canada and beyond.*One of our methods mimics DFT and gives a computational speed-up of *4 to 6 orders of magnitude. It will allow the study of nanoalloys*with potential applications in catalysis and data storage devices.*Taking clues from our recent discovery of bimetallic cages,*we will search for new and bigger all-metal cages.**Minima of the PES are equilibrium geometries of molecules; saddle points are*transition states; steepest descent lines connecting saddle points to minima are reaction paths;*low energy regions in the vicinity of steepest-descent lines are important*for detailed models of reaction mechanisms. We will continue to make*expert use of quantum chemistry and density functional theory*(DFT), combined with our own computer codes, to investigate PES. **Students will get trained in research projects that combine method development*and applications and will acquire a variety of skills: expertise in UNIX*and quantum chemistry software, programming and shell scripting, mathematical*modeling, and general scientific literacy. The projects are designed at*various levels to address the needs and capabilities of undergraduate, *postgraduate, and postdoctoral students.**We will work on three fronts to study nanoalloys that have interesting*properties and potential use in catalysis and information technologies.** (1) Global optimization. Evolutionary computing methods, like Genetic*Algorithms (GA), will be developed to determine the geometric structure*of nanoalloy clusters.** (2) Reaction mechanisms. We have used Particle Swarm Optimization (PSO)*to discover, without human supervision, the sequence of geometric transformations*that occur in molecules during chemical reactions (``reaction mechanisms''). We will*create a new method, based on chemical intuition and optimization techniques, to find a priori*(without any DFT calculation) reaction mechanisms. We will find, on a *case-by-case basis, whether this mechanism is a good approximation to the*lowest-energy reaction path (the true mechanism), and will classify chemical reactions accordingly.** (3) Atomistic simulations. We developed a new fitting method for creating*high-dimensional PES that is fully automated, does not require*the user to input a function form, and which works for practically any*chemical composition. This PES function mimics an accurate method (DFT) and offers a*speed-up of 4 to 6 orders of magnitude relative to DFT. We will use it to carry out*accurate Monte Carlo (AIMC) simulations where the PES is used with "importance sampling"*to give great computational speed-up. We will also take a two-pronged approach*to global optimization where we use the PES function for screening*a large number of geometric structures and generate a much smaller subset*for which the DFT energy gets calculated.**Working on those three fronts we will try to uncover the principles that*govern the relative stability and geometric structure, and the magnetic,*electronic and chemical properties of bimetallic clusters. Based on these*principles, and novel methods unique to our group, we will design stable*nanoalloys for possible applications in catalysis and magnetic*data storage devices.