Interplay between electronic and atomic structure in expanded fluid potassium: a path-integral molecular dynamics study

The interplay between the electronic and atomic structure is studied for expanded supercritical fluid potassium using the method of path integral molecular dynamics. Upon expansion of liquid potassium, a transition occurs at nearly two times the critical density. As density decreases to that density, the fluid retains the properties of a metal with electron correlation enhancing its kinetic energy relative to the free electron gas. The calculated enhancement in kinetic energy is described adequately by the Hubbard model. As density and atomic coordination decrease, there is evidence for the formation of diamagnetic spin-paired electronic species. The computer simulation results are shown to be in good qualitative agreement with available experimental data for another alkali fluid, namely cesium.