Collaborative Research: Petascale Simulations of Quantum Systems by Stochastic Methods: Tools and Applications

该奖项支持开发、测试和优化新一代模拟代码，用于在Petascale计算机上计算电子态。这些代码将基于量子蒙特卡罗方法。这一努力将结合计算机科学的最新进展，如全局阵列、容错并行、图形处理单元和任务动态并行，以及可以治疗相关电子系统和研究目前遥不可及的物理效应的最新学科进展。目标是建立生产质量的量子蒙特卡罗代码，可以利用第一轨道和后续硬件来实现科学突破计算。成功使用千万亿级计算机可能是非常具有挑战性的。将量子蒙特卡罗代码放大两个数量级以上将需要为算法组织和并行化寻找新的途径；例如，利用节点的多核/共享内存性质。对容错和负载均衡的关注将导致可靠和高效的Petascale码。一个关键的推力将是将电子的量子蒙特卡罗方法与离子的经典模拟方法结合起来，使之能够在几乎任何系统上进行真实的模拟。新的预测能力和洞察力将产生，特别是使用电子的完整量子力学描述来研究动力学和有限温度现象。另一个推动力涉及将量子蒙特卡罗应用于强关联电子系统--这是凝聚态物理学中最重要的挑战之一。PI计划实现和测试新的相关波函数，如带有回流的pfaffian，以及新的量子蒙特卡罗算法，如经典自由度和量子自由度的动态耦合。这些发展将应用于研究水，在没有任何经验或平均场输入的情况下，对所有相关自由度进行完整的量子力学描述，如非零温度下的电子和质子。量子蒙特卡罗计算也将被用来理解过渡金属化合物，特别是过渡金属氧化物材料中的磁态和高压下的金属-绝缘体转变。尽管经过了几十年的研究，这些系统仍然没有得到充分的了解，需要极高的精度才能揭示各种多体现象和实验观察到的现象的起源。科学界将通过开源项目QMCPACK和QWalk获得开发的计算工具。全局阵列工具包将提供基于全局地址空间编程模型的高级和可伸缩编程环境。这项研究和开发工作还将支持高性能计算领域的研究生和博士后培训。PIS将组织一个名为“Petaflop量子蒙特卡罗方法”的暑期班，以培训学生、博士后和研究人员使用所开发的方法，使他们能够在Petascale和更高级别的高性能计算方面开辟新的领域。非技术摘要该奖项支持针对最强大的计算机开发、测试和调整新一代计算机代码的性能。这些新代码将基于量子力学，并创建一种在原子尺度上探测材料的“虚拟显微镜”。这些代码将通过对电子及其运动的准确量子力学描述，提供对原子之间作用力的准确确定，这是这些作用力的最终来源。由此产生的代码将用于研究水，水可能是生命中最重要的组成部分，但也是最具挑战性的液体和固体之一。PI代码对电子的准确描述将使对材料的最准确的计算研究成为可能，这些材料涉及相互作用强烈的电子，从而产生新的物质状态。了解这些材料可能会导致发现新的物质状态，从而可能导致新的材料和设备技术。开发的代码将提供给更广泛的计算科学家社区，并使他们能够利用最强大的计算机开辟新的领域。这项研究和开发工作还将支持高性能计算领域的研究生和博士后培训。PIS将组织一个名为“Petaflop量子蒙特卡罗方法”的暑期班，以培训学生、博士后和研究人员使用所开发的方法，并使他们能够在千万亿级利用高性能计算开辟新的领域。

TECHNICAL SUMMARY This award supports developing, testing, and optimizing a new generation of simulation codes for calculating electronic states on petascale computers. The codes will be based on quantum Monte Carlo methods. The effort will combine recent advances in computer science, such as Global Arrays, fault-tolerant parallelism, Graphics Processing Units and task-dynamical parallelism, with recent disciplinary advances that can treat correlated electronic systems and study physical effects currently out of reach. The goal is to establish production-quality quantum Monte Carlo codes that can exploit Track I and follow-on hardware to achieve scientific breakthrough calculations. Successful use of petascale computers will likely be very challenging. Scaling up the quantum Monte Carlo codes by more than two orders of magnitude will require pursuing new avenues for algorithm organization and parallelization; for example, utilizing the multicore/shared memory nature of the nodes. Attention to fault tolerance and load balance will lead to reliable and efficient petascale codes. A key thrust will be to couple quantum Monte Carlo methods for electrons with classical simulation methods for the ions enabling realistic simulations on virtually any system. New predictive capabilities and insights will result, particularly into dynamics and finite temperature phenomena using a full quantum mechanical description of the electrons. Another thrust involves applying quantum Monte Carlo to strongly correlated electronic systems - among the most important challenges in condensed matter physics. The PIs plan to implement and test new correlated wavefunctions such as pfaffians with backflow, and new quantum Monte Carlo algorithms, such as the dynamical coupling of classical and quantum degrees of freedom. These developments will be applied to study water with a full quantum mechanical description of all the relevant degrees of freedom such as electrons and protons at nonzero temperatures without any empirical or mean-field inputs. Quantum Monte Carlo calculations will also be used to understand transition metal compounds, in particular, the magnetic states and metal-insulator transitions at high pressures in transition metal oxide materials. Despite decades of studies these systems remain inadequately understood and require exceedingly high accuracy to reveal the origins of a variety of many-body phenomena and experimentally observed phenomena. The developed computational tools will be available to the scientific community through the open source projects QMCPACK, and QWalk. The Global Arrays toolkit will provide a high-level and scalable programming environment based on the global address space programming model. This research and development effort will also support training of graduate students and postdocs in the area of high performance computing. The PIs will organize a Summer School, "Petaflop Quantum Monte Carlo Methods," to train students, postdocs and researchers in the developed methodologies and enable them to open new frontiers with high performance computing at the petascale and beyond. NONTECHNICAL SUMMARY This award supports developing, testing, and tuning the performance of a new generation of computer codes targeted for the most powerful computers. These new codes will be based on quantum mechanics and create a "virtual microscope" that probe materials at the atomic scale. These codes will provide an accurate determination of the forces between atoms enabled by an accurate quantum mechanical description of the electrons and their motions which are the ultimate sources of these forces. The resulting code will be applied to study water, perhaps the most important component of life but also one of the most challenging liquids and solids to understand. The accurate description of electrons afforded by the PIs codes will enable the most accurate computational study of materials which involve electrons that interact strongly with each other leading to new states of matter. Understanding these materials may lead to the discovery of new states of matter that may lead to new materials and device technologies. The codes that are developed will be made available to the broader computational community of scientists and empower them to utilize the most powerful computers to open new frontiers. This research and development effort will also support training of graduate students and postdocs in the area of high performance computing. The PIs will organize a Summer School, "Petaflop Quantum Monte Carlo Methods," to train students, postdocs and researchers in the developed methodologies and enable them to open new frontiers with high performance computing at the petascale.