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Size-consistent explicitly correlated triple excitation correction.

Mihály Kállay1, Réka A Horváth1, László Gyevi-Nagy1

  • 1Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, P.O. Box 91, Budapest H-1521, Hungary.

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Summary
This summary is machine-generated.

A novel size-consistent method reduces errors in explicitly correlated coupled-cluster calculations. This computationally efficient approach improves accuracy for various molecular properties.

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Area of Science:

  • Computational chemistry
  • Quantum chemistry
  • Theoretical chemistry

Background:

  • Explicitly correlated coupled-cluster methods, particularly CCSD(T), are benchmarks for quantum chemistry.
  • Basis set incompleteness error (BSSE) is a known issue affecting the accuracy of triple excitation corrections.
  • Existing methods for addressing BSSE in triple excitations may lack size consistency.

Purpose of the Study:

  • To develop a new, size-consistent approach to mitigate basis set incompleteness error in the perturbative triples correction.
  • To offer an approximation that is computationally efficient and easy to implement.

Main Methods:

  • The proposed method is based on the intuitive triples correction approach but modified for size consistency.
  • The new approximation is integrated into explicitly correlated coupled-cluster singles and doubles with perturbative triples (CCSD(T)) calculations.
  • Performance is evaluated by comparing results with conventional (T) corrections.

Main Results:

  • The new method effectively reduces basis set incompleteness error in triple excitation corrections.
  • Calculations of atomization, reaction, and interaction energies, bond lengths, and vibrational frequencies show improved accuracy.
  • The size-consistent nature of the new approach is demonstrated and validated.

Conclusions:

  • The proposed size-consistent approximation offers a practical and efficient way to improve the accuracy of explicitly correlated coupled-cluster calculations.
  • This method provides a valuable tool for high-accuracy computational chemistry, particularly for systems where BSSE is significant.