The efficient calculation of electron impact ionization cross sections with effective core potentials.

Area of Science:

• Atomic and Molecular Physics
• Quantum Chemistry
• Computational Physics

Background:

• Electron impact ionization is crucial for understanding molecular behavior.
• Accurate calculation of ionization cross sections is computationally demanding, especially for heavy-atom molecules.
• Existing methods may lack accuracy for complex molecular targets.

Purpose of the Study:

• To implement and validate a Binary Encounter Bethe (BEB) model incorporating an effective core potential (ECP) procedure.
• To efficiently calculate electron impact ionization cross sections for molecules containing heavy atoms.
• To assess the impact of ECPs and target molecule polarizability on ionization cross section predictions.

Main Methods:

• A black-box Binary Encounter Bethe (BEB) method was employed.
• An effective core potential (ECP) procedure was integrated for computational efficiency.
• Calculations were performed using the Quantemol electron collisions software (UKRMol+ codes).
• Tested on various series of molecules including CF4, CCl4, CH4, SiH4, PH3, PF3, SiCl4, BCl3, CH3Br, and CF3I.

Main Results:

• The ECP approach generally increased predicted ionization cross sections at lower energies.
• ECP-based BEB calculations showed improved agreement with experimental data compared to all-electron methods.
• Scaling BEB cross sections by target molecule polarizability yielded inconsistent improvements in agreement with experimental data.

Conclusions:

• The implemented ECP-BEB method provides an efficient and more accurate approach for calculating electron impact ionization cross sections for heavy-atom molecules.
• ECPs are beneficial for improving low-energy ionization cross section predictions.
• Polarizability scaling is not a universally reliable method for enhancing BEB cross section accuracy.