Solving a problem with a single parameter: a smooth bcc to fcc phase transition for metallic lithium.

Density functional calculations for metallic lithium along a cuboidal bcc-to-fcc transformation path demonstrate that the bcc phase is quasi-degenerate with the fcc phase with a very small activiation barrier of 0.1 kJ mol -1 , but becomes the dominant phase at higher temperatures in accordance with Landau theory. This resolves the long-standing controversy about the two phases for lithium.