Quantum-solid behavior and the electronic structure of the light alkali metals

The identification of the 9R rhombohedral phase for the low-temperature structure of lithium offers a possible resolution of observed disparities in its optical properties and new experimental opportunities for a direct determination of the electron-ion interaction. The latter is central to the construction of effective ion-ion interactions which in turn control both lattice statics and dynamics and the ultimate choice of structure. The static 9R phase, whose Jones zone is actually quite ``spheroidal,'' appears electronically favored by a Hume-Rothery argument. The lattices are, however, far from static; nevertheless, the most important of the dynamic effects can still be incorporated within the definition of state-dependent effective potentials acting between quasistatic ions. From these a possible physical source of the driving force of the transition can be identified.