  We propose a mixed analytical-ab-initio method for the accurate calculation
of the conductance in monovalent atomic wires. The method relies on the most
general formula for ballistic transport through a monovalent wire, whose
parameters can be determined from first-principles calculations. Our central
result is the demonstration of the highly non-universal behavior of the
conductance, which depends on the fine details of the contacts to the leads. We
are therefore able to reconcile a large number of the apparently contradictory
results that have recently appeared in the literature.
