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Seniority zero pair coupled cluster doubles theory.

Tamar Stein1, Thomas M Henderson1, Gustavo E Scuseria1

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This summary is machine-generated.

Pair coupled cluster doubles (p-CCD) offers a computationally efficient method for describing electron correlation. Optimizing orbitals enhances p-CCD

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Area of Science:

  • Quantum chemistry
  • Computational physics
  • Theoretical chemistry

Background:

  • Coupled cluster theory with single and double excitations (CCSD) excels at weak electron correlation but struggles with strong static correlation.
  • Pair coupled cluster doubles (p-CCD) is a simplified method focusing on pair excitations, preserving seniority.
  • p-CCD offers computational efficiency approaching mean-field cost.

Purpose of the Study:

  • To demonstrate the accuracy of orbital-optimized p-CCD for static correlation.
  • To analyze the contribution of seniority sectors to coupled cluster doubles (CCD) correlation energy.
  • To explore extensions of CCD for strongly correlated systems.

Main Methods:

  • Demonstration with numerous examples.
  • Analysis of correlation energy contributions across different seniority sectors.
  • Investigation using Hartree-Fock and Brueckner orbitals.
  • Exploration of orbital localization effects.

Main Results:

  • Orbital optimization makes p-CCD an excellent approximation to full configuration interaction (FCI) for the paired space.
  • Optimized p-CCD accurately describes static correlation.
  • Methods are shown to retain Brueckner orbital properties at the p-CCD level.
  • Contributions of seniority sectors to CCD correlation energy are explored.

Conclusions:

  • Optimized p-CCD provides a highly accurate and computationally feasible method for static correlation.
  • Understanding seniority sector contributions aids in developing better correlated electron system models.
  • Further research into extending CCD methods is promising for strongly correlated systems.