  So far, it represents a challenging task to reproduce angle-resolved
photoelectron (ARPES) spectra of epitaxial silicene by first-principles
calculations. Here, we report on the resolution of the previously controversial
issue related to the structural configuration of silicene on the ZrB$_2$(0001)
surface and its band structure. In particular, by representing the band
structure in a large Brillouin zone associated with a single Si atom, it is
found that the imaginary part of the one-particle Green's function follows the
spectral weight observed in ARPES spectra. By additionally varying the in-plane
lattice constant, the results of density functional theory calculations and
ARPES data obtained in a wide energy range converge into the "planar-like"
phase and provide the orbital character of electronic states in the vicinity of
the Fermi level. It is anticipated that the choice of a smaller commensurate
unit cell for the representation of the electronic structure will be useful for
the study of epitaxial two-dimensional materials on various substrates in
general.
