: Specify the particles and physical processes (electromagnetic, hadronic, etc.) to be simulated.
The true "geant4 manual" for daily simulation work is the . This exists both as a downloadable PDF and an interactive web version on the Geant4 website. geant4 manual
For medical physics (MeV range), start with G4EmStandardPhysics_option4 . For high-energy LHC work, use FTFP_BERT . Never build your own physics list from scratch unless you have a dedicated reason. geant4 manual