The nonequilibrium dynamics of correlated many-particle systems is of interest in connection with pump–probe experiments on molecular systems and solids, as well as theoretical investigations of transport properties and relaxation processes. Nonequilibrium Green's functions are a powerful tool to study interaction effects in quantum many-particle systems out of equilibrium, and to extract physically relevant information for the interpretation of experiments. We present the open-source software package NESSi (The Non-Equilibrium Systems Simulation package) which allows to perform many-body dynamics simulations based on Green's functions on the L-shaped Kadanoff–Baym contour. NESSi contains the library libcntr which implements tools for basic operations on these nonequilibrium Green's functions, for constructing Feynman diagrams, and for the solution of integral and integro-differential equations involving contour Green's functions. The library employs a discretization of the Kadanoff–Baym contour into time N points and a high-order implementation of integration routines. The total integrated error scales up to O(N−7), which is important since the numerical effort increases at least cubically with the simulation time. A distributed-memory parallelization over reciprocal space allows large-scale simulations of lattice systems. We provide a collection of example programs ranging from dynamics in simple two-level systems to problems relevant in contemporary condensed matter physics, including Hubbard clusters and Hubbard or Holstein lattice models. The libcntr library is the basis of a follow-up software package for nonequilibrium dynamical mean-field theory calculations based on strong-coupling perturbative impurity solvers. Program summary: Program Title: NESSi CPC Library link to program files: http://dx.doi.org/10.17632/973crf9hgd.1 Licensing provisions: MPL v2.0 Programming language: C++, python External routines/libraries: cmake, eigen3, hdf5 (optional), mpi (optional), omp (optional) Nature of problem: Solves equations of motion of time-dependent Green's functions on the Kadanoff–Baym contour. Solution method: Higher-order solution methods of integral and integro-differential equations on the Kadanoff–Baym contour.

中文翻译：

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NESSi：非平衡系统仿真包

相关多粒子系统的非平衡动力学与分子系统和固体的泵-探针实验以及输运特性和弛豫过程的理论研究有关。非平衡格林函数是研究非平衡量子多粒子系统中的相互作用效应和提取物理相关信息以解释实验的强大工具。我们提供了开源软件包 NESSi（非平衡系统仿真包），它允许基于 L 形 Kadanoff-Baym 轮廓上的格林函数执行多体动力学仿真。NESSi 包含库 libcntr，它实现了对这些非平衡格林函数进行基本操作的工具，用于构建费曼图，以及求解涉及等高格林函数的积分和积分微分方程。该库采用将 Kadanoff-Baym 轮廓离散化为时间 N 点和积分例程的高阶实现。总积分误差放大到 O(N−7)，这很重要，因为数值工作至少随模拟时间三次增加。互易空间上的分布式内存并行化允许对格系统进行大规模模拟。我们提供了一系列示例程序，从简单的两级系统中的动力学到当代凝聚态物理学中的相关问题，包括哈伯德星团和哈伯德或荷斯坦晶格模型。libcntr 库是基于强耦合微扰杂质求解器的非平衡动态平均场理论计算的后续软件包的基础。程序摘要： 程序名称：NESSi CPC 库程序文件链接：http://dx.doi.org/10.17632/973crf9hgd.1 许可条款：MPL v2.0 编程语言：C++、python 外部例程/库：cmake、eigen3 , hdf5（可选），mpi（可选），omp（可选） 问题性质：求解 Kadanoff-Baym 等高线上与时间相关的格林函数的运动方程。求解方法：Kadanoff-Baym 等高线上积分和积分微分方程的高阶求解方法。1 许可条款：MPL v2.0 编程语言：C++、python 外部例程/库：cmake、eigen3、hdf5（可选）、mpi（可选）、omp（可选） 问题性质：求解与时间相关的格林运动方程Kadanoff-Baym 等高线上的函数。求解方法：Kadanoff-Baym 等高线上积分和积分微分方程的高阶求解方法。1 许可条款：MPL v2.0 编程语言：C++、python 外部例程/库：cmake、eigen3、hdf5（可选）、mpi（可选）、omp（可选） 问题性质：求解与时间相关的格林运动方程Kadanoff-Baym 等高线上的函数。求解方法：Kadanoff-Baym 等高线上积分和积分微分方程的高阶求解方法。