From generalized-valence-bond calculations on numerous Li-atom clusters (${\mathrm{Li}}_n$ and ${{\mathrm{Li}}_n}^{+}$, $n<~13$), we conclude that the optimum bonding involves singly occupied orbitals localized interstitially (in tetrahedra). Rules based on the calculations are used to predict low-energy isomers (leading for ${\mathrm{Li}}_{13}^{+}$ to low-symmetry structures that are significantly more stable than the icosahedron but retain local fivefold-symmetry axes) and are applied to infinite metallic systems.

• Received 23 May 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.2563