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Open-shell extensions to closed-shell pCCD.

Katharina Boguslawski1

  • 1Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Toruń, ul. Grudziądzka 5, 87-100 Toruń, Poland. k.boguslawski@fizyka.umk.pl.

Chemical Communications (Cambridge, England)
|November 5, 2021
PubMed
Summary
This summary is machine-generated.

We extended the pair coupled cluster doubles (pCCD) method to accurately describe open-shell molecules, which are typically challenging for this approach. Our new methods achieve chemical accuracy at a modest computational cost.

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Area of Science:

  • Quantum Chemistry
  • Computational Chemistry
  • Theoretical Chemistry

Background:

  • The pair coupled cluster doubles (pCCD) ansatz is an efficient single-reference method for multi-reference problems.
  • However, standard pCCD is limited to closed-shell systems.
  • Describing open-shell molecules accurately is crucial in computational chemistry.

Purpose of the Study:

  • To extend the pCCD ansatz to handle open-shell molecules.
  • To enable the accurate calculation of electronic structure for systems with unpaired electrons.
  • To provide a computationally inexpensive yet accurate alternative for open-shell systems.

Main Methods:

  • Development of novel extensions to the pCCD ansatz.
  • Application of these extensions to open-shell molecules with up to 4 unpaired electrons.
  • Comparison of performance against established methods like DMRG and CCSD(T).

Main Results:

  • The extended pCCD methods successfully target open-shell molecules.
  • The approach achieves near chemical accuracy for challenging cases.
  • Computational cost remains modest, making it an attractive option.

Conclusions:

  • The developed extensions significantly broaden the applicability of pCCD.
  • This advancement offers a cost-effective route to accurate electronic structure calculations for open-shell systems.
  • The new methods show promise comparable to more computationally demanding techniques.