The electronic structures of nanosystems: Calculating the ground states of sodium nanoclusters and the actuation of carbon nanotubes

This contribution reports large scale electronic structure calculations for two important classes of nanosystems, namely metal nanoclusters and carbon nanotubes. In the former case we focus on the ground-state structure of sodium cluster anions which is obtained by solving the Kohn-Sham equations of density functional theory (DFT) in combination with an efficient genetic optimisation algorithm. The accuracy and efficiency of this approach is reflected in the electronic density of states of the lowest lying isomer showing excellent agreement with experimental photoelectron spectra. In the case of the carbon nanotubes (CNTs), the swelling and shrinking of the CNT paper due to electron or hole injection (bond strength induced actuation) has been studied. Experimentally, the charging of the tubes is caused by a small applied voltage and it is compensated by a electrochemical double layer formed in a surounding liquid electrolyte. Here we focus on models describing a singel nanotubes and the double layer within density functional and density functional based tight-binding band structure calculations. We show that the frequently used representation of the double layer by a jellium background reveals an unphysical dependence of the CNT actuation on the size of the computational box. As an alternative a cylindrical charge compensation, not suffering of this shortcoming, is suggested.