TRIQS/Nevanlinna: Implementation of the Nevanlinna Analytic Continuation method for noise-free data

TL;DR

The paper introduces TRIQS/Nevanlinna, an open-source implementation of the Nevanlinna analytic continuation method, offering high accuracy for spectral functions with sharp features, as an alternative to maximum entropy methods.

Contribution

It provides a new, efficient open-source software package implementing the Nevanlinna analytic continuation method with Hardy functions optimization for improved spectral resolution.

Findings

Accurately resolves wide band and sharp spectral features.

Offers a high-quality open-source alternative to maximum entropy methods.

Integrates seamlessly with TRIQS framework and electronic structure tools.

Abstract

We present the TRIQS/Nevanlinna analytic continuation package, an efficient implementation of the methods proposed by J. Fei et al in [Phys. Rev. Lett. 126, 056402 (2021)] and [Phys. Rev. B 104, 165111 (2021)]. TRIQS/Nevanlinna strives to provide a high quality open source (distributed under the GNU General Public License version 3) alternative to the more widely adopted Maximum Entropy based analytic continuation programs. With the additional Hardy functions optimization procedure, it allows for an accurate resolution of wide band and sharp features in the spectral function. Those problems can be formulated in terms of imaginary time or Matsubara frequency response functions. The application is based on the TRIQS C++/Python framework, which allows for easy interoperability with other TRIQS-based applications, electronic band structure codes and visualization tools. Similar to other TRIQS packages, it comes with a convenient Python interface.