Electronic Entropy, Shell Structure, and Size-Evolutionary Patterns of Metal Clusters

We show that electronic-entropy effects in the size-evolutionary patterns of relatively small (as small as 20 atoms), simple-metal clusters already become prominent at moderate temperatures. Detailed agreement between our finite-temperature--shell-correction-method calculations and experimental results is obtained for certain temperatures. This agreement includes a size-dependent smearing out of fine-structure features, accompanied by a measurable reduction of the heights of the steps marking major-shell and subshell closings, thus allowing for a quantitative analysis of cluster temperatures.