Ionic structure and photoabsorption in medium-sized sodium clusters

We present ground-state configurations and photoabsorption spectra of $\mathrm{Na}-7+,$ $\mathrm{Na}-27+,$ and $\mathrm{Na}-41+.\mathrm{}$ Both the ionic structure and the photoabsorption spectra of medium-size sodium clusters beyond Na-20 have been calculated self-consistently with a nonspherical treatment of the valence electrons in density-functional theory. We use a local pseudopotential that has been adjusted to experimental bulk properties and the atomic $3s$ level of sodium. Our studies have shown that both the ionic structure of the ground state and the positions of the plasmon resonances depend sensitively on the pseudopotential used in the calculation, which stresses the importance of its consistent use in both steps.