Electronic Structure of Condensed Matter

9802373塞珀利这项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化系统，如均匀电子气，以及原子、分子和凝聚态物质中的现实问题。所采用的方法是量子蒙特卡罗(QMC)模拟和密度泛函理论(DFT)的结合。对于某些多体问题，QMC可以提供精确的结果，并且这种方法的适用范围正在扩大。离散傅里叶变换是对真实系统进行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面，这是算法精度的限制因素。发展了一种动态优化节面的方法，并将应用于多电子系统。工作还将继续使用QMC方法计算力。第一个应用将是研究电子气体中质子之间的作用力。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被用来研究激子、双激子和超导状态的形成；以及金属中的氢杂质，这是密度泛函理论的检验，也是材料科学中的一个重要问题。关于高压下氢的物相的新工作将集中在使用贝里的物相公式预测红外活性上。还将发展研究相关系统中介电极化的一般理论方法。对新想法的第一次测试正在格子模型中实施，并将为真实系统开发方法。多体计算将被用来测试近似的DFT泛函并推导出新的形式。长期的挑战是开发算法来解决著名的“符号问题”，这是蒙特卡罗方法应用于费米子和动力学的一个限制因素；开发超越近似DFT方法的健壮的“N阶”线性标度方法；以及将这些方法应用于突出的材料问题。这项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化系统，如均匀电子气，以及原子、分子和凝聚态物质中的现实问题。长期的挑战是开发算法来解决著名的“符号问题”，这是蒙特卡罗方法应用于费米子和动力学的一个限制因素；开发超越近似DFT方法的健壮的“N阶”线性标度方法；以及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. ***