Finite size corrections to the conductance of ballistic wires

The dependence of the conductance of ballistic wires on the work function of different metals is analyzed. We show that quantum finite-size effects can be taken into account by a simple correction to the Sharvin formula. Although the conductance is suppressed relative to the classical Sharvin limit, the correction is much smaller than that obtained from calculations based on ''hard-wall'' boundary conditions. Different sources of errors in the determination of actual cross sections in atomic-scale contacts from conductance measurements are discussed.