First-principles studies of the thermodynamic properties of bulk Li

We have calculated the electronic structure and the vibrational properties of bulk Li in the fcc and bcc structures using large super-cells and an ab initio, non-local pseudopotential approach with a plane-wave expansion. The method is based on the density functional theory with core corrections and local exchange and correlation effects. The calculated phonon dispersion curves for the bcc structure are compared with the neutron scattering data. The difference between the Helmholtz free energies for the bcc and the closed-packed structures, in the harmonic approximation, is found to be small for the temperature range of interest. The zero-point energies for both structures are substantial, while the heat capacity differential displays a switch at around 90 K.