Second order Møller-Plesset and coupled cluster singles and doubles methods with complex basis functions for...

Area of Science:

• Theoretical Chemistry
• Quantum Chemistry
• Computational Physics

Background:

• Molecular resonances are crucial for understanding electron-molecule interactions.
• Accurate computation of these resonances requires advanced theoretical methods.
• Correlated levels of theory are essential for describing complex electronic structures.

Purpose of the Study:

• To apply the complex basis function method to molecular resonances.
• To compute accurate Siegert energies for shape resonances in small molecules.
• To investigate the accuracy of complex potential energy surfaces and explore Feshbach resonances.

Main Methods:

• Complex basis function method.
• Second-order Møller-Plesset perturbation theory (MP2).
• Equation-of-motion electron attachment coupled-cluster singles and doubles (EOM-EA-CCSD) methods.
• Analytic continuation of complex θ-trajectories.

Main Results:

• Accurate Siegert energies were computed for N₂⁻, CO⁻, CO₂⁻, and CH₂O⁻.
• Energy differences on θ-trajectories provided more consistent results than total energies.
• The study investigated the accurate computation of complex potential energy surfaces.

Conclusions:

• The complex basis function method, combined with correlated electronic structure methods, accurately computes molecular resonances.
• EOM-EA-CCSD shows promise for studying Feshbach resonances, as explored in e-helium scattering.
• This work advances the theoretical understanding and prediction of electron-molecule interactions.