  The structural, electronic, and optical properties of twelve multicomponent
oxides with layered structure, RAMO$_4$, where R$^{3+}$=In or Sc; A$^{3+}$=Al
or Ga; and M$^{2+}$=Ca, Cd, Mg, or Zn, are investigated using first-principles
density functional approach. The compositional complexity of RAMO$_4$ leads to
a wide range of band gap values varying from 2.45 eV for InGaCdO$_4$ to 6.29 eV
for ScAlMgO$_4$. Strikingly, despite the different band gaps in the oxide
constituents, namely, 2-4 eV in CdO, In$_2$O$_3$, or ZnO; 5-6 for Ga$_2$O$_3$
or Sc$_2$O$_3$; and 7-9 eV in CaO, MgO, or Al$_2$O$_3$, the bottom of the
conduction band in the multicomponent oxides is formed from the s-states of all
cations and their neighboring oxygen p-states. We show that the hybrid nature
of the conduction band in multicomponent oxides originates from the unusual
five-fold atomic coordination of A$^{3+}$ and M$^{2+}$ cations which enables
the interaction between the spatially-spread s-orbitals of adjacent cations via
shared oxygen atoms. The effect of the local atomic coordination on the band
gap, the electron effective mass, the orbital composition of the conduction
band, and the expected (an)isotropic character of the electron transport in
layered RAMO$_4$ is thoroughly discussed.
