Please replace the description with this corrected version. Minor corrections.
Since their invention, carbon nanotubes (CNT), which can be both semiconducting as well as metallic, have been postulated to have interesting active device aspects. For example, heterojunctions, made of two CNTs of different chiralities joined together through an interface of topological defects, have been associated with rectifying diode behavior. Determination of meaningful structures of these interfaces constitutes a major part of the study of such heterojunctions. In principle, any two CNTs of different chiralities can be joined through a single pentagon-heptagon pair, often forming a kinked interface, resulting in highly bent heterojunctions. Here we present a tool that renders the structure of linear heterojunctions between two CNTs of different chiralities but similar radii, joined together through an interface that may require more than one pentagon-heptagon defect. Subsequently, within a nearest neighbor tight-binding approximation, the tool provides density of states and zero bias transmission as a function of energy, calculated assuming semi-infinite CNT electrodes of matching chiralities on the two sides of the heterojunction.