Temperature-dependent ionization potential of sodium clusters

The ionization potential of sodium clusters (8 less than or equal to N less than or equal to 55) at a finite temperature is studied using density functional theory and ab initio molecular dynamics. The threshold regions of the photoionization efficiency curves are deduced from the integrated IP distributions, which are obtained from the energy eigenvalues of the highest occupied Kohn-Sham states during molecular dynamics by applying a theoretically well-defined shift. The calculated ionization potentials are directly compared to the experimental values. The energetically best geometry of Na-55 is found to be a slightly distorted icosahedron.