  We perform first principles band calculation of the newly discovered
superconductor LaO$_{1-x}$F$_x$BiS$_2$, and study the lattice structure and the
fluorine doping dependence of the gap between the valence and conduction bands.
We find that the distance between La and S as well as the fluorine doping
significantly affects the band gap. On the other hand, the four orbital model
of the BiS$_2$ layer shows that the lattice structure does not affect this
portion of the band. Still, the band gap can affect the carrier concentration
in the case of light electron doping, which in turn should affect the transport
properties.
