Non-equilibrium divide-and-conquer method for nanoscale simulations

在这个由化学系化学理论、模型和计算方法计划资助的项目中，加州大学圣地亚哥分校的迈克尔·加尔佩林教授正在开发新的方法，以提供模拟纳米级设备行为的理论框架。对这类系统的兴趣源于它们的技术前景和基本物理特性。该项目的目标是解决理论化学的核心挑战之一：准确预测纳米系统的电子性质及其对外部扰动的反应。这可以通过预测理论在分子水平上对这种装置进行理解。这些结果是开发记忆和逻辑分子器件、基于分子的传感器、用于太阳能转换的光伏和新型电子产品的核心。这项研究将不同的科学界联系在一起的能力使参与该项目的学生能够参与灵活的课程，从而为他们在基础科学或应用科学、学院或国家实验室、多体理论、分子光谱学和计算量子化学的一个领域或界面工作做好准备。纳米尺度开放非平衡系统的理论模拟大多采用单粒子基函数(例如，在非平衡格林函数密度泛函理论(NEGF-DFT)方法中的轨道)。这些方法允许处理实际大小的系统，但在处理系统内强烈的相互作用时变得不方便。另一种方法，非平衡原子极限(如伪粒子(PP)或Hubbard NEGF)，利用孤立系统的多体状态作为基础，这允许考虑系统的相互作用。这种配方的适用性仅限于相对较小的体系。该项目开发了一种方法，非平衡分而治之方法，它利用了这两种方法的优点：NEGF-DFT处理大系统的能力，PP和Hubbard NEGF准确解释强烈的局部相互作用的能力。对原始系统(无论是在实空间还是在状态空间)的划分被用单粒子或多体状态方法处理的部分来使用。这将通常的分而治之的方法扩展到开放的非平衡量子系统领域。这些结果是开发记忆和逻辑分子器件、基于分子的传感器、用于太阳能转换的光伏和新型电子产品的核心。

In this project funded by the Chemical Theory, Models and Computational Methods program in the Division of Chemistry, Professor Michael Galperin, of the University of California, San Diego, is developing new methods to provide the theoretical framework to simulate the behavior of nanoscale devices. Interest in such systems stems from their technological promise and fundamental physical properties. The goal of the project is to resolve one of the central challenges of theoretical chemistry: accurate prediction of the electronic properties of nanoscale systems and their response to external perturbations. This can lead to an understanding of such devices at the molecular level with predictive theory. The results are central in developing memory and logic molecular devices, molecule-based sensors, photovoltaics for solar conversion and new types of electronics. The ability of the research to interconnect different scientific communities allows students involved in the project to participate in a flexible curriculum, thus preparing them to work in either fundamental or applied sciences, in academy or in national labs, in one of the fields or at interfaces of many-body theory, molecular spectroscopy, and computational quantum chemistry.Theoretical simulations of nanoscale open non-equilibrium systems mostly employ single-particle basis functions (e.g. orbitals as in the non-equilibrium Green function density functional theory (NEGF-DFT) approach). These approaches allow treatment of systems of realistic sizes, but become inconvenient in treating strong intra-system interactions. An alternative approach, the non-equilibrium atomic limit (e.g. the pseudoparticle (PP) or Hubbard NEGF), utilizes many-body states of the isolated system as a basis, which allows accounting for the system interactions. The applicability of such formulations is limited to relatively small systems. The project develops a methodology, the non-equilibrium divide-and-conquer method, which capitalizes on the strong sides of both methodologies: the NEGF-DFT ability to treat big systems and the PP and Hubbard NEGF ability to account for strong local interactions exactly. Partitioning of the original system (either in real or state space) is utilized with the parts treated by either single-particle or many-body states approaches. This extends the usual divide-and-conquer methodology to the realm of open non-equilibrium quantum systems. The results are central in developing memory and logic molecular devices, molecule-based sensors, photovoltaics for solar conversion and new types of electronics.