Ferromagnetic instabilities in atomically thin lithium and sodium wires

Using density functional theory, the ground‐state structural, electronic, and magnetic properties of monoatomic 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 ferromagnetic, which can be traced to exchange effects arising from occupation of the second subband as a function of the interatomic distance.