Structural phase stability and electron-phonon coupling in lithium

First-principles calculations of the foe energy of several structural phase s of Li are presented. The density-functional linear-response approach is u sed to calculate the volume-dependent phonon frequencies needed for computi ng the vibrational free energy within the quasiharmonic approximation. We s how that the transformation from a close-packed structure at low temperatur es to the bce phase upon heating is driven by the large vibrational entropy associated with low-energy phonon modes in bcc Li. In addition, we find th at the strength of the electron-phonon interaction in Li is strongly depend ent on crystal structure. The coupling strength is significantly reduced in the low-temperature close-packed phases as compared to the bcc phase, and is consistent with the observed lack of a superconducting transition in Li.