Electronic Structure of Condensed Matter

[802373] Ceperley本研究的长期目标是发展实用、有效的理论方法来准确预测多电子系统的性质。理论方法和计算算法正在产生，可以应用于重要的理想系统，如均相电子气体，以及原子，分子和凝聚态物质的现实问题。所采取的方法是量子蒙特卡罗（QMC）模拟和密度泛函理论（DFT）的结合。QMC可以为一些多体问题提供精确的结果，该方法的应用范围正在不断扩大。DFT是真实系统大规模仿真的唯一可行方法。研究目标包括发展QMC方法，重点是改进费米子波函数的节点表面，这是限制算法精度的因素。本文提出了一种动态优化节点表面的方法，并将其应用于多电子系统。工作还将继续用QMC方法计算力。首先应用于电子气体中质子间的作用力。QMC方法在物理问题上的应用将包括纳米级量子器件和低维系统；电子-空穴等离子体，其中有限温度技术将用于研究激子，双激子和超导态的形成；金属中的氢杂质，这是对DFT的检验，也是材料科学中的一个重要问题。高压下氢相的新研究将集中在利用Berry相公式预测红外活动上。研究相关系统中介电极化的一般理论方法也有待发展。新想法的第一次测试正在晶格模型中实施，并将为实际系统开发方法。多体计算将用于测试近似DFT泛函并导出新的形式。长期的挑战是开发算法来解决著名的“符号问题”，这是限制蒙特卡罗方法应用于费米子和动力学的一个因素；开发超越近似DFT方法的鲁棒“n阶”线性标度方法；并将这些方法应用于突出的材料问题。本研究的长远目标是发展实用、有效的理论方法来准确预测多电子系统的性质。理论方法和计算算法正在产生，可以应用于重要的理想系统，如均相电子气体，以及原子，分子和凝聚态物质的现实问题。长期的挑战是开发算法来解决著名的“符号问题”，这是限制蒙特卡罗方法应用于费米子和动力学的一个因素；开发超越近似DFT方法的鲁棒“n阶”线性标度方法；并将这些方法应用于突出的材料问题。＊＊＊

9802373 Ceperley The long range goal of this research is to develop practical, efficient theoretical methods to accurately predict the properties of many-electron systems. Theoretical methods and computational algorithms are being generated that can be applied to important idealized systems, such as the homogeneous electron gas, as well as to realistic problems in atoms, molecules, and condensed matter. The approach taken is a combination of quantum Monte Carlo (QMC) simulations and density functional theory (DFT). QMC can provide exact results for some many-body problems and the range of problems for which this method can be applied is being extended. DFT is the only method feasible for large-scale simulations of real systems. Research objectives include the development of QMC methods with emphasis on the improvement of the nodal surfaces for fermion wavefunctions which is the limiting factor in the accuracy of the algorithms. A method has been developed to dynamically optimize the nodal surface and will be applied to many-electron systems. Work will also continue to calculate forces with QMC methods. First applications will be for forces between protons in an electron gas. Applications of QMC methods to physical problems will include nanoscale quantum devices and lower dimensional systems; electron-hole plasmas where finite-temperature techniques will be used to srudy the formation of excitons, bi-excitons, and the superconducting state; and hydrogen impurities in metals, which is a test of DFT and an important problem in materials science. New work on the phases of hydrogen at high pressure will focus on prediction of infrared activity using the Berry's phase formulation. Also to be developed will be general theoretical methods for studying dielectric polarization in correlated systems. The first test of the new ideas are being implemented in lattice models and methods will be developed for real systems. Many- body calculations will be used to test approximate DFT functionals and to derive new forms. Long term challenges are to develop algorithms to solve the famous "sign problem" which is a limiting factor in application of Monte Carlo methods to fermions and dynamics; to develop robust "order-N' linear scaling methods that go beyond approximate DFT methods; and to apply these methods to outstanding materials problems. %%% The long range goal of this research is to develop practical, efficient theoretical methods to accurately predict the properties of many-electron systems. Theoretical methods and computational algorithms are being generated that can be applied to important idealized systems, such as the homogeneous electron gas, as well as to realistic problems in atoms, molecules, and condensed matter. Long term challenges are to develop algorithms to solve the famous "sign problem" which is a limiting factor in application of Monte Carlo methods to fermions and dynamics; to develop robust "order-N' linear scaling methods that go beyond approximate DFT methods; and to apply these methods to outstanding materials problems. ***