We develop a new hadronic model for GEANT4 that is specialized for the disintegration of the deuteron by photons, dγ → np. For the description of two-nucleon interactions, we employ a pionless effective field theory with dibaryon fields (dEFT). We apply the new model of GEANT4 (G4dEFT) to the calculations of the total and the differential cross sections in dγ → np and compare the results with empirical data. As an application of the new model, we calculate the neutron yield from the γ + CD 2 process. G4dEFT predicts peaks for the neutron yield, but the existing model of GEANT4 does not show such behavior.