  Band structure is theoretically studied in partially flattened carbon
nanotubes within an effective-mass scheme. Effects of inter-wall interactions
are shown to be important in non-chiral nanotubes such as zigzag and armchair
and can essentially be neglected in chiral nanotubes except in the close
vicinity of non-chiral tubes. In fact, inter-wall interactions significantly
modify states depending on relative displacement in the flattened region in
non-chiral tubes and can convert semiconducting tubes into metallic and vice
versa. They diminish rapidly when the chiral angle deviates from that of the
zigzag or armchair tube, although the decay is slower in the vicinity of
armchair tubes.
