Molecular shape, capacitance, and chemical hardness

To elucidate the effects of overall molecular shape upon the electronic res ponse properties of molecules and nanoclusters we recently have considered various jellium duster models for the mean excitation energy. Here we apply similar models to characterize the relationship among gross molecular shap e, the capacitance of an identically shaped spheroidal conductor, and the c hemical hardness of the system eta = (I - A)/2 (I, A are the first ionizati on energy and electron affinity, respectively). As with the mean excitation energies, the models possess reasonable predictive capability for these ca ses. Within a strict density functional interpretation we also show that, q uite unlike a classical capacitor, the capacitance of a nanoscale object is not independent of the way charge is added. Classical behavior is recovere d by an average over the final charge state of the nanoscale capacitor. (C) 2000 John Wiley & Sons, Inc.