IMFP data can be collected from the National Institute of Standards and Technology (NIST) Electron Inelastic-Mean-Free-Path Database or the NIST Database for the Simulation of Electron Spectra for Surface Analysis (SESSA). The data contains IMFPs determined by EPES for energies below 2 keV. Otherwise, IMFPs can be determined from the TPP-2M or the S1 formula.