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Pyqcm: An open-source Python library for quantum cluster methods

by Théo N. Dionne, Alexandre Foley, Moïse Rousseau, David Sénéchal

Submission summary

Authors (as registered SciPost users): David Sénéchal
Submission information
Preprint Link: https://arxiv.org/abs/2305.18643v2  (pdf)
Code repository: https://bitbucket.org/dsenechQCM/qcm_wed.git
Date accepted: 2023-11-21
Date submitted: 2023-10-17 04:41
Submitted by: Sénéchal, David
Submitted to: SciPost Physics Codebases
Ontological classification
Academic field: Physics
Specialties:
  • Condensed Matter Physics - Computational
Approaches: Theoretical, Computational

Abstract

Pyqcm is a Python/C++ library that implements a few quantum cluster methods with an exact diagonalization impurity solver. Quantum cluster methods are used in the study of strongly correlated electrons to provide an approximate solution to Hubbard-like models. The methods covered by this library are Cluster Perturbation Theory (CPT), the Variational Cluster Approach (VCA) and Cellular (or Cluster) Dynamical Mean Field Theory (CDMFT). The impurity solver (the technique used to compute the cluster's interacting Green function) is exact diagonalization from sparse matrices, using the Lanczos algorithm and variants thereof. The core library is written in C++ for performance, but the interface is in Python, for ease of use and inter-operability with the numerical Python ecosystem. The library is distributed under the GPL license.

Author comments upon resubmission

This resubmission takes into account comments by the two referees, as indicated in their reports and in comments posted by us in response to their reports. The new section 5.8 added has required some time to write because of the new plots and computations required.

List of changes

• A reference to material on which this paper is based (mostly lecture notes from a summer school, 2008) has been added.
• Fig. 1 has been modified as per the referees' suggestions.
• Fig. 2 has been modified to show G and M scheme periodizations, in 3D plots
• Comments on the hypothesis of existence/uniqueness of the self-energy functional (after Eq. 107) have been added.
• Sect. 5.8 has been added (issues with VCA) , with two new figures
• A short new section (7) has been inserted on the respective merits of CPT, VCA and CDMFT.
• Table 3 (performance tests) has been redone
• The paper is now compatible with version 2.2 of the pyqcm library

Published as SciPost Phys. Codebases 23 (2023) , SciPost Phys. Codebases 23-r2.2 (2023)


Reports on this Submission

Report #2 by Anonymous (Referee 4) on 2023-11-10 (Invited Report)

Report

All questions and remarks of the other referee and myself have been answered and taken into account in the revised version of the manuscript.
Sections 5.8 and 7 have been added and provide valuable additional information on the limitations and the pros and cons of the respective quantum cluster techniques. Together with the rest of the paper, this information will prove very useful for future users of the pyqcm code.
I strongly recommend the publication of the manuscript in SciPost Physics Codebases.

The source installation of the current version of the code (v. 2.2) worked fine on a compute cluster using an Intel compiler.

Minor remark:
-two typos that might need correction in the 3rd paragraph of the new section 7: "to me more" -> to be more ; "convergence issues grows" -> grow.

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Report #1 by Anonymous (Referee 3) on 2023-10-27 (Invited Report)

Report

The authors have answered my questions and accordingly revised the manuscript.
I think this is a very useful code package, including good explanations.
I fully support the publication of this manuscript in SciPost.

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