Structure of chiral single-walled carbon nanotubes under hydrostatic pressure

We investigate the structural parameters, i.e., bond lengths and bond angles of chiral tubes of various chiralities using a procedure based on helical and rotational symmetries and Tersoff potential. The results indicate that at ambient conditions, there are equal bond lengths and three unequal bond angles in the structure of chiral tubes. This bond length depends significantly on the chirality and insignificantly on the tube radius. Length of the tubes does not play very significant role on bond length and bond angles. These C–C bonds were recalculated under hydrostatic pressure. The bond length compresses with pressure while the bond angles remain practically unchanged. We also carry out analysis regarding the cross sectional shape of chiral tubes and its pressure dependence. It is found that at some pressures, transition from circular to oval cross section takes place. The transition pressure is found to strongly depend on the radius and chirality of tube. At this transition, corresponding to given elliptical cross section, the bond length for all chiral tubes of various chiralities and radius approaches nearly a fixed value of 1.434 Å.