  This paper constructs the mapping relation from density of states (DOS) to
UV-vis spectra by using an ab initio perspective. Taking BiOIO3 semiconductor
photocatalyst as an example, the experimental verification was also carried
out. The optical response of the material considers the superposition benefits
of all possible transitions. Directly using the difference between valence band
maximum (VBM) and conduction band minimum (CBM) will lead to an underestimate
of the energy band gap. This paper provides a new idea of linking the density
functional theory (DFT) data with experiment phenomenon.
