  We present first-principles band calculations as well as structural
optimization of the orthorhombic K$_1$C$_{60}$ polymerized phase. We found
three-dimensional inter-fullerene bonding/anti-bonding characters consisting of
$t_{1u}$ molecular orbitals with $p$-like symmetry in the conduction bands. The
formation of the four-membered ring connecting the fullerenes lifts the $p_x$
band from the continuous $p_y$-$p_z$ band, where the z-axis is parallel to the
chain. The asymmetry between $p_x$ and $p_y$ may play an important role in
binding the chains with the rotational configuration proposed by Stephens et
al.
