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An efficient implementation of time-dependent linear-response theory for strongly orthogonal geminal wave function

Michał Hapka1, Katarzyna Pernal2, Hans Jørgen Aa Jensen3

  • 1Faculty of Chemistry, University of Warsaw, ul. L. Pasteura 1, 02-093 Warsaw, Poland.

The Journal of Chemical Physics
|May 7, 2022
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Summary

We implemented time-dependent generalized valence bond (TD-GVB) methods for calculating molecular excitation energies. TD-GVB shows limited improvement over time-dependent Hartree-Fock for dynamic correlation but struggles with double excitations.

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Area of Science:

  • Quantum Chemistry
  • Computational Chemistry
  • Theoretical Chemistry

Background:

  • Strongly orthogonal geminal wave function models offer a computationally tractable approach to electron correlation.
  • Accurate prediction of molecular excitation energies is crucial for understanding photophysical processes.

Purpose of the Study:

  • To implement and evaluate time-dependent linear-response equations for time-dependent generalized valence bond (TD-GVB) perfect-pairing theory.
  • To assess the accuracy of TD-GVB for calculating singlet excitation energies in small and medium-sized molecules.

Main Methods:

  • Developed an efficient direct iterative approach to solve linear-response equations for TD-GVB.
  • Employed a restricted-step second-order algorithm for optimizing geminal wave functions, including a novel black-box initial orbital generation scheme.
  • Calculated singlet excitation energies for various molecular systems.

Main Results:

  • TD-GVB provides only a marginal improvement over time-dependent Hartree-Fock for systems dominated by dynamic correlation.
  • TD-GVB significantly underestimates or overestimates excitation energies for states heavily influenced by double excitations when compared to linear-response complete active space self-consistent field (LR-CASSCF).

Conclusions:

  • The current TD-GVB implementation shows limitations in accurately describing states with significant double excitation character.
  • Further development is needed to improve the performance of geminal-based methods for complex electronic excitations.