Ab initio study of the dielectric response of crystalline ropes of metallic single-walled carbon nanotubes: Tube-diameter and helicity effects

The dielectric-response functions of crystalline ropes of metallic single-walled carbon nanotubes were determined from time-dependent density-functional theory in the random-phase approximation. Interband transitions and plasmonic excitations were studied as a function of momentum transfer. The impact of the tube diameter was shown for the (n,n) armchair-type series (n ranging from 3 to 8) covering a diameter range from 4 to 11 Å. Helicity effects were examined for the thinnest tubes, the armchair (3,3) versus the zigzag (5,0) configurations. Our results give detailed insight into the various kinds of excitations that can be observed in ropes of nanotubes. Recent experimental findings and trends by electron energy loss and Raman spectroscopies are reproduced and explained.