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This study introduces a new computational method, complex-energy RI-CC2, for accurately calculating electronic resonances in molecules. The method shows improved agreement with experimental data for temporary anions compared to existing techniques.

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Area of Science:

  • Quantum Chemistry
  • Computational Physics
  • Theoretical Spectroscopy

Background:

  • Electronic resonances are crucial metastable states in molecular processes.
  • Traditional Hermitian quantum mechanics struggles to accurately describe resonances and their continuum coupling.
  • Non-Hermitian quantum mechanics offers a framework using complex energies to model these states.

Purpose of the Study:

  • To develop and evaluate novel complex-energy methods for studying electronic resonances.
  • To investigate the performance of the resolution-of-the-identity coupled cluster method with second-order approximation (RI-CC2) for electronic resonances.
  • To assess the accuracy of the electron-attachment variant (EA-CC2) for computing negative electron affinities and resonance widths.

Main Methods:

  • Combined complex absorbing potential and complex basis functions with the RI-CC2 method.
  • Employed the electron-attachment (EA) variant of RI-CC2 for calculations.
  • Compared RI-CC2 results with equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) and experimental data for various molecules.

Main Results:

  • EA-CC2 accurately computes negative electron affinities and decay widths for temporary anions.
  • EA-CC2 shows better agreement with experimental data for negative electron affinities than EOM-EA-CCSD across studied molecules.
  • Resonance widths calculated by EA-CC2 are consistently smaller than those from EOM-EA-CCSD, aligning better with experiments.

Conclusions:

  • The complex-energy RI-CC2 method provides a computationally efficient and accurate approach for studying electronic resonances.
  • EA-CC2 is a reliable tool for investigating temporary anions and their properties.
  • The findings advance the understanding and computational treatment of electronic resonances in quantum chemistry.