Density functional calculation of the photoabsorption spectrum of simple metal clusters: Beyond the local-density approximation and jellium model

The time-dependent density functional theory has been used to calculate the photoabsorption spectrum of small alkali metal clusters, for which comparison with experiments is possible. Most theoretical works have used firstly the local density approximation for exchange and correlation effects and secondly the jellium model to simulate the ionic background. In this paper we use the spherically averaged pseudopotential model to introduce geometric effects, and the weighted-density approximation to account for non-local exchange-correlation effects. The influence of these effects is analysed for neutral and charged clusters of alkali metals and considerably improved predictions are obtained.