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，描述分子的能量如何随着分子的几何结构变化而变化的数学函数)，从而为研究分子结构和化学反应能力提供了*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*，并用于模拟具有数百个原子的系统。这些工具*将对加拿大和其他地方的研究人员非常重要。*我们的一种方法模拟了DFT，使计算速度提高了*4到6个数量级。它将允许研究纳米合金*在催化和数据存储设备中的潜在应用。*从我们最近发现的双金属笼子中获得线索*我们将寻找新的和更大的全金属笼子。**PES的迷你是分子的平衡几何结构；鞍点是*过渡态；连接鞍点到最小值的最陡峭的下降线是反应路径；*最陡峭下降线附近的低能区是重要的*反应机理的详细模型。我们将继续利用量子化学和密度泛函理论(DFT)的专家知识，结合我们自己的计算机代码来研究PES。**学生将接受将方法开发*和应用程序相结合的研究项目的培训，并将获得各种技能：在Unix*和量子化学软件、编程和外壳脚本编写、数学*建模和一般科学素养方面的专业知识。这些项目设计在不同的层次上，以满足本科生、研究生和博士后的需求和能力。**我们将在三个方面工作，研究具有有趣*性质和在催化和信息技术中潜在应用的纳米合金。**(1)全局优化。进化计算方法，如遗传*算法(GA)，将被开发来确定纳米合金团簇的几何结构。**(2)反应机理。我们已经使用粒子群优化(PSO)*在没有人类监督的情况下发现了化学反应期间分子中发生的几何变换*的序列(“反应机理”)。我们将创造一种新的方法，基于化学直觉和优化技术，寻找先验的*(不需要任何密度泛函计算)反应机理。我们将在逐个案例的基础上，找出这个机制是否是*最低能量反应路径(真正的机制)的良好近似，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，它是完全自动化的，不需要*用户输入函数形式，并且几乎适用于任何*化学成分。此PES函数模拟精确方法(DFT)，并提供相对于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“重要性抽样”*一起使用，以提供极大的计算速度。我们还将采取双管齐下的方法*进行全局优化，我们使用PES函数来筛选*大量的几何结构，并生成一个小得多的子集*来计算DFT能量。**在这三个方面工作，我们将试图揭示*支配双金属团簇的相对稳定性和几何结构以及磁性、电子和化学性质的原理。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，可能应用于催化和磁*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.