  Most elemental metals under ambient conditions adopt simple structures such
as BCC, FCC and HCP in specific groupings across the Periodic Table, and on
compression, many of these elements undergo transitions to surprisingly complex
structures, including open and low-symmetry phases not expected from
conventional free-electron based theories of metals. First-principles
calculations have been able to reproduce many observed structures and
transitions, but a unified, predictive theory of bonding that underlies this
behavior is not yet in hand. We propose a remarkably simple theory based on
large-scale high-throughput calculations of the elements over a broad range of
thermodynamic conditions. The results broaden the conventional concept of
metallic bonding with a new perspective that both explains the stability of
different simple structures as well as lower symmetry phases arising from
electron localization at interstitial sites in these structures. The success of
this simple framework reveals the important role of chemical interactions in
governing the structures and electronic properties of simple metals.
