Spectral evolution of four different SNe Ia explosion models in rest-frame wavelengths. Columns from left to right: W7, N100, subCh, and merger models. Rows from top to bottom: rest-frame time after explosion in days, as indicated on the right of each row. In early phases (≲10 days after explosions), the spectra of different SNe Ia models show distinguishing features that depend on assumptions in the radiative transfer calculations, whereas at later times the spectra from different models start to resemble one another.