Direct dark matter detection experiments such like CDEX, CDMSlite collaborations pursue the searches with germanium detectors at low energy region. Measurements indicate one of the main background sources is originated from high energy gammas through Compton scattering and its spectra appears the step structures at electronic orbital energies. The result has contradiction with classical Compton model. In reality, high energy gammas interact with the bound electrons in atoms in terrestrial detectors. The low energy Compton scattering theory is depended on impulse Approximation framework. This work aims at low energy spectra via atomic Compton scattering models in Geant4 software. The work has been carried out the comparison of Livermore model, Penelope model as well as Monash model in the simulation framework. The ratios of the step structure at K-shell are 95.92%, 92.87%, 96.68%, respectively, which reflects the bound electron effect. Spectra at sub-keV energy region demonstrates a 10% discrepancy among those models.
