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New schemes for internally contracted multi-reference configuration interaction.

Yubin Wang1, Huixian Han2, Yibo Lei3

  • 1Institute of Modern Physics, Northwest University, Xi'an, Shaanxi 710069, China.

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Summary
This summary is machine-generated.

This study introduces a new internally contracted multi-reference configuration interaction (MRCI) method, simplifying calculations by treating orbitals uniformly. This approach overcomes previous limitations, enhancing computational efficiency for electronic structure studies.

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Area of Science:

  • Quantum Chemistry
  • Computational Chemistry
  • Theoretical Chemistry

Background:

  • Multi-reference configuration interaction (MRCI) is crucial for accurate electronic structure calculations.
  • Existing MRCI methods can be computationally intensive, especially with a large number of internal orbitals.
  • The graphical unitary group approach (GUGA) is a powerful tool for simplifying CI calculations.

Purpose of the Study:

  • To develop a new, more efficient internally contracted MRCI (ic-MRCI) scheme.
  • To simplify the calculation of coupling coefficients and CI matrix elements.
  • To overcome the bottleneck of the number of internal orbitals in MRCI calculations.

Main Methods:

  • Application of the graphical unitary group approach (GUGA).
  • Utilizing hole-particle symmetry to split Distinct Row Tables (DRTs) into sub-DRTs.
  • Defining contractions as linear combinations of arcs within sub-DRTs.

Main Results:

  • A novel ic-MRCI scheme was successfully developed.
  • The new scheme treats closed-shell (hole) and external orbitals uniformly, simplifying calculations.
  • Energies calculated with the new code closely match those from the established WK code in MOLPRO.
  • The new code demonstrates competitive computational efficiency.

Conclusions:

  • The new ic-MRCI scheme is valid and efficient.
  • This method significantly simplifies MRCI calculations and removes the limitation imposed by the number of internal orbitals.
  • The developed code offers advantages in computational efficiency for electronic structure studies.