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arXiv · 2604.22223

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

Seongjun Mo·Dongming Li·Mancheon Han·Johan Jönsson·Byungkyun Kang·Hoonkyung Lee·Gabriel Kotliar·Sangkook Choi
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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.

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Seongjun Mo, Dongming Li, Mancheon Han, Johan Jönsson, Byungkyun Kang, Hoonkyung Lee, Gabriel Kotliar, Sangkook Choi. 2026-04-24. QAssemble: A Pure Python Package for Quantum Many-Body Theory. https://arxiv.org/abs/2604.22223

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