Q&A_QEC: Vertical Excitation Energy Cutoff

Q: What is the difference between the vertical excitation energy cutoff, start energy and end energy in close coupling (CC) calculations in QEC? 

A: The start and end energy grid define the energies of the incoming scattering electron. The vertical energy cutoff defines an energy cutoff for the inclusion of excited states in the close coupling calculation. If no vertical energy cutoff is selected, QEC will include all the excited states below the ionisation potential calculated from Koopman’s (HOMO energy) ionisation potential. Alternatively, the number of states can be used to limit the number of excited states included in the close coupling expansion of the target.

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