Relativistic effects, phonons, and the isostructural transition in cesium

Abstract

Relativistic linear-muffin-tin-orbital calculations of the fcc cesium 0-K pressure-volume isotherm are reported which indicate that the isostructural transition in this material is a more complicated phenomenon than has been thought to be the case. It is shown that the effect of relativistic shifts on the electron bands serves to eliminate the possibility of obtaining such a transition in the $T=0\mathrm{}$ isotherm for the static lattice. Thermal effects must therefore play an essential role in the observed isostructural transition at room temperature. In particular, it is suggested on the basis of simple model calculations that an anomaly in the lattice vibrational contribution to the pressure, which is in fact intimately connected with the electronic transition in cesium, is a possible mechanism for the observed transition.