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 func tional theory and ab initio molecular dynamics. The threshold regions of th e photoionization efficiency curves are deduced from the integrated IP dist ributions, which are obtained from the energy eigenvalues of the highest oc cupied Kohn-Sham states during molecular dynamics by applying a theoretical ly well-defined shift. The calculated ionization potentials are directly co mpared to the experimental values. The energetically best geometry of Na-55 is found to be a slightly distorted icosahedron.