Absence of metal clusters and appearance of new electron states inNa6C60

We calculate the structural and electronic properties of the ${\mathrm{Na}}_6$ ${\mathrm{C}}_{60}$ fulleride using the Car-Parrinello method as well as standard local density approximation band structure calculations. In contrast to previous claims we find that metal clusters do not form but, like the potassium and rubidium fullerides, sodium intercalation gives rise to a conventional ionic compound. Unlike the case of heavier alkali fullerides, a characteristic new kind of low-lying electron state appears that is not the ${\mathrm{C}}_{60}$ state. Effects of temperature on the electronic nature of the compound are discussed as well as consequences of these findings for higher fullerides.