Pseudopotential Calculation of Phonon Frequencies and Grüneisen Parameters for Lithium

Phonon frequencies and Gr\"uneisen parameters are calculated from a local pseudopotential model for bcc lithium. Two pseudopotential parameters and a Born-Mayer repulsive potential parameter were adjusted to fit the measured crystal binding energy, lattice spacing, and compressibility; in this fitting procedure the Born-Mayer repulsive energy turned out to be essentially zero. The phonon frequencies are in good qualitative agreement with experiment, except that the crossing of longitudinal and transverse branches along the [001] direction is not reproduced by the theory. The Kohn anomalies are too small to be seen in the calculated phonon frequency curves, but are apparent in the Gr\"uneisen-parameter curves.