Coupled-cluster theory for positron binding in anions and polyatomic molecules

Area of Science:

• Quantum Chemistry
• Computational Physics
• Molecular Modeling

Background:

• Positron binding energies are essential for understanding electron-positron interactions.
• Accurate theoretical methods are needed to model these systems.
• Existing methods may not fully capture electron correlation effects.

Purpose of the Study:

• To develop and present the positron coupled cluster singles and doubles (POS-CCSD) method.
• To calculate positron binding energies in various molecular systems.
• To investigate the role of electron correlation and nuclear relaxation in positron attachment.

Main Methods:

• The POS-CCSD method treats electrons and positrons equally, including double-electron-single-positron excitations.
• Benchmarking was performed on atomic anions and polyatomic systems (polar and non-polar).
• Results were compared with quantum Monte Carlo, multi-reference configuration interaction, and experimental data.

Main Results:

• POS-CCSD results for H- binding energies show excellent agreement with other advanced theoretical methods.
• Quantitative agreement with experimental data was not achieved due to slow convergence with basis set size.
• The study highlights the importance of electron correlation for accurate electron-positron system descriptions.
• Nuclear relaxation effects following positron attachment were examined in LiH.

Conclusions:

• The POS-CCSD method provides a robust framework for calculating positron binding energies.
• Electron correlation plays a critical role in accurately describing electron-positron systems.
• Further basis set optimization is needed for quantitative agreement with experimental data.