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

A black box Binary Encounter Bethe (BEB) with an effective core potential (ECP) procedure is implemented, which facilitates the efficient calculation of electron impact ionization cross sections for molecules that include heavy atoms. This is available in the Quantemol electron collisions software, a user friendly graphical user interface to the UKRMol+ codes. Tests were performed for the following series of molecules: CF₄, CCl₄, CBr₄, CI₄, and CAt₄; CH₄, SiH₄, GeH₄, and SnH₄; PH₃, PF₃, and PCl₃; SiCl₄ and BCl₃; and CH₃Br and CF₃I. Use of an ECP generally raises the predicted ionization cross section at lower energies leading to improved agreement with experiment compared to all electron calculations for BEB cross sections. Scaling BEB cross sections by the polarizability of the target molecule is shown to give somewhat erratic results, which do not always provide closer agreement with the measured cross sections.