Calculation of the Total Energy and Pressure of Compressed Cesium

The results of a self-consistent $X\alpha$ augmented-plane-wave calculation of the cohesive energy, pressure, and enthalpy of bcc and fcc cesium metal are presented. The exchange factor used was approximately the one which made the total atomic $X\alpha$ energy equal to the total atomic Hartree-Fock energy. The maximum value of the cohesive energy was calculated to be 0.062 ± 0.0015 Ry, and it occurs when the volume of the primitive unit cell is 780 ± 30 cubic atomic units. These results can be compared with the experimental values of 0.062 Ry and 745 cubic atomic units. The computed pressure and enthalpy predict that the isomorphic transition of the fcc phase of cesium should occur at 26 ± 2 kbar at 0°K. The computed isomorphic transition is accompanied by severe distortion of the Fermi surface, as suggested by Yamashita and Asano and by Kmetko.