New Concepts of Metallic Bonding Based on Valence-Bond Ideas

From generalized-valence-bond calculations on numerous Li-atom clusters (Liₙ and Liₙ⁺, $n<~13$), 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 Li₁₃⁺ 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.