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Unphysical solutions in coupled-cluster-based random phase approximation and how to avoid them.

Ruiheng Song1, Xiliang Gong1, Hong-Zhou Ye1,2

  • 1Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.

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|October 22, 2025
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Summary
This summary is machine-generated.

This study addresses unphysical solutions in direct ring coupled-cluster doubles (drCCD)-based random phase approximation (RPA) methods. We developed a validation criterion and improved preconditioners to stabilize drCCD calculations for various chemical systems.

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Area of Science:

  • Quantum Chemistry
  • Computational Chemistry
  • Electronic Structure Theory

Background:

  • Direct ring coupled-cluster doubles (drCCD)-based random phase approximation (RPA) is a powerful computational framework.
  • A known issue involves unphysical solutions, limiting its applicability, especially for small-gap systems.

Purpose of the Study:

  • To investigate the origin of multi-solution issues in drCCD.
  • To develop methods for validating drCCD solutions and improving their stability.

Main Methods:

  • Elucidation of the underlying cause of multi-solution problems in drCCD.
  • Development of a practical validation criterion for drCCD solutions.
  • Implementation of improved preconditioners using level shifting and regularized MP2 methods.

Main Results:

  • The study successfully identified the origin of the multi-solution issue in drCCD.
  • A robust validation criterion and effective preconditioners were developed.
  • The approach demonstrated effectiveness on challenging systems like stretched bonds, conjugated systems, and metallic clusters.

Conclusions:

  • The developed methods enhance the reliability and applicability of drCCD-based RPA.
  • This work provides a foundation for stable, large-scale applications of advanced RPA methods.
  • The approach is extendable to various advanced RPA formulations.