Predicted lithium-boron compounds under high pressure.

High pressure can fundamentally alter the bonding patterns of light elements and their compounds, leading to the unexpected formation of materials with unusual chemical and physical properties. Using an unbiased structure search method based on particle-swarm optimization algorithms in combination with density functional theory calculations, we investigate the phase stabilities and structural changes of various Li-B systems on the Li-rich regime under high pressures. We identify the formation of four stoichiometric lithium borides (Li(3)B(2), Li(2)B, Li(4)B, and Li(6)B) having unforeseen structural features that might be experimentally synthesizable over a wide range of pressures. Strikingly, it is found that the B-B bonding patterns of these lithium borides evolve from graphite-like sheets in turn to zigzag chains, dimers, and eventually isolated B ions with increasing Li content. These intriguing B-B bonding features are chemically rationalized by the elevated B anionic charges as a result of Li→B charge transfer.