  The electron-transport properties of single-row monoatomic nanowires made of
5$d$ elements are examined by first-principles calculations based on the
density functional theory. We found that oscillation patterns with a period
longer than two-atom length are dominant in the conductance of Ir and Pt
monoatomic nanowires, although the transmission of the $s$-$d_{z^2}$ channel
still exhibits even-odd oscillatory behavior. When the nanowires are deformed
into zigzag configurations from the straight configuration, the oscillation
behavior of the patterns with long periods changes and the oscillations
eventually disappear. On the other hand, the even-odd oscillatory behavior of
the $s$-$d_{z^2}$ channel still survives even in the deformed nanowire. The
even-odd oscillation in the conductance of Ir and Pt nanowires is interpreted
to be due to the low sensitivity of the oscillation of the $s$-$d_{z^2}$
channel to the spatial deformation of the nanowires.
