  Using density functional theory the ground state structural, electronic, and
magnetic properties of monatomic lithium and sodium chains with low average
density are investigated. A metallic, zigzag ground state structure is
predicted but, most interestingly, stable equilibria for chains under tension
are predicted to be {\it ferromagnetic}, which can be traced to exchange
effects arising from occupation of the second subband as a function of the
interatomic distance.
