First Principles Study of Work Functions of Single Wall Carbon Nanotubes
  We performed first principles calculations on work functions of single wall carbon nanotubes (SWNTs), which can be divided into two classes according to tube diameter (D). For class I tubes (D > 1 nm), work functions lie within a narrow distribution (~0.1 eV) and show no significant chirality or diameter dependence. For class II tubes (D < 1 nm), work functions show substantial changes, with armchair tubes decrease monotonously with diameter, while zigzag tubes show opposite trend. Surface dipoles and hybridization effects are shown to be responsible for the observed work function change. 
Bin Shan, and Kyeongjae Cho