Calculation of the electronic transition in cesium

The behavior of cesium under compression is unusual not only because of the isostructural transition at 4.25 GPa, but also because of the abnormal softness of the isotherm at lower pressures. Self-consistent augmented-plane-wave $X\alpha$ calculations of the $T=0\mathrm{}$, fcc cesium pressure-volume isotherm are reported which suggest that both phenomena may be due to the electronic $s-d$ transition in this material. It is demonstrated that in the vicinity of an electronic transition, such techniques are very poorly convergent with the number of points taken in the Brillouin zone, and that great care must be exercised to insure that the results are physically meaningful.