Discrete Lehmann representation of imaginary time Green's functions

@article{Kaye2022DiscreteLR,
  title={Discrete Lehmann representation of imaginary time Green's functions},
  author={Jason Kaye and Kun Chen and Olivier Parcollet},
  journal={ArXiv},
  year={2022},
  volume={abs/2107.13094}
}
We present an efficient basis for imaginary time Green’s functions based on a low rank decomposition of the spectral Lehmann representation. The basis functions are simply a set of well-chosen exponentials, so the corresponding expansion may be thought of as a discrete form of the Lehmann representation using an effective spectral density which is a sum of δ functions. The basis is determined only by an upper bound on the product βωmax, with β the inverse temperature and ωmax an energy cutoff… 
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