NESSi: The Non-Equilibrium Systems Simulation package
Artikel i vetenskaplig tidskrift, 2020

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: 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.

Numerical simulations

Nonequilibrium dynamics of quantum many-body problems

Kadanoff–Baym equations

Keldysh formalism


Michael Schüler

Stanford University

Université de Fribourg

Denis Golež

Université de Fribourg

Flatiron Institute

Yuta Murakami

Université de Fribourg

Tokyo Institute of Technology

Nikolaj Bittner

Université de Fribourg

Andreas Herrmann

Université de Fribourg

Hugo Strand

Chalmers, Fysik, E-commons

Flatiron Institute

Philipp Werner

Université de Fribourg

Martin Eckstein

Friedrich-Alexander-Universität Erlangen Nurnberg (FAU)

Computer Physics Communications

0010-4655 (ISSN)

Vol. 257 107484



Den kondenserade materiens fysik


C3SE (Chalmers Centre for Computational Science and Engineering)



Mer information

Senast uppdaterat