Ground states of potassium adsorbate on single-walled carbon nanotubes

We have investigated the ground states of single-walled carbon nanotubes with potassium atoms adsorbed in the center of the hexagonal unit using the Monte-Carlo method and the first-principles approach. We predict that two types of high coverage structures (x=1/2,2/3) are stable for adsorption on the (6,0) carbon nanotube in addition to low coverage structures of adsorbate on graphite. It is shown that the curvature of carbon nanotube surface enhances the stability of high coverage structures of adsorbate.