QAssemble: A Pure Python Package for Quantum Many-Body Theory

TL;DR

QAssemble is a modular, pure-Python package for quantum many-body calculations, offering efficient implementations of various approximations validated on graphene and a five-orbital model.

Contribution

It introduces a unified, object-oriented Python framework with optimized kernels for quantum many-body problems, enabling both efficiency and extensibility.

Findings

Achieves up to 60x speedup over traditional methods.

Successfully models electronic structure of graphene with local and non-local interactions.

Demonstrates efficiency of vectorized kernels and Lehmann representation in Python.

Abstract

QAssemble is a pure-Python package for the quantum many-body problem. It implements various functional approaches, such as tight-binding, Hartree-Fock, and GW approximations within a unified object-oriented architecture. Each physical concept--crystal structure, Hamiltonian, Green's function, self-energy, polarizability, screened Coulomb interaction--is represented as a distinct class. The modular design prioritizes code clarity and extensibility, leveraging NumPy, SciPy, and libdlr for numerical operations. Performance-critical kernels, including the polarizability bubble, Dyson equation inversion, and lattice Fourier transforms, are systematically vectorized and combined with the discrete Lehmann representation to achieve practical efficiency within a pure-Python environment. We validate QAssemble on the electronic structure of graphene with local and non-local interactions. Furthermore, benchmarks on a five-orbital extended Hund-Hubbard model demonstrate that this strategy delivers up to a 60x speedup over traditional loop-based Matsubara implementations. QAssemble supports both batch execution for production calculations and interactive workflows for method development.