Abstract
In order to better explain the observed late-time (or nebular, hereafter) spectra of Type Ia supernovae, we are working on constructing a model which includes the major physical processes involved in the spectral generation, (i.e., the gamma-ray energy deposition following the Ni-Co-Fe radioactive decays, the thermal structure and ionization balance determined by various atomic collision channels, and the radiative transport of the final emergent photons). Because the eventual success of the model depends highly on the general availability and accuracy of the atomic data (especially of the iron group elements, such as the radiative transition probabilities and the electron impact excitation/ionization, electron-ion recombination, photoionization, and charge transfer rates) relevant to the calculation of the thermal structure and ionization balance, we have searched, updated and even partly recalculated the data set which was used in our previous work. The ultimate goal is to set up a 3-D synthetic spectral model of the nebular phase in conjunction with the major 3-D explosion simulations of Type Ia supernovae.