  We describe a semi-empirical atomic basis Extended H\"uckel Theoretical (EHT)
technique that can be used to calculate bulk bandstructure, surface density of
states, electronic transmission and interfacial chemistry of various materials
within the same computational platform. We apply this method to study multiple
technologically important systems, starting with carbon-nanotubes (CNT) and
their interfaces in this paper, and silicon-based heterostructures in our
follow-up paper. We find that when it comes to quantum transport through
interesting, complex heterostructures, the Huckel bandstructure offers a fair
and practical compromise between orthogonal tight-binding theories (OTB) with
limited transferability between environments under large distortion, and
density functional theories (DFT) that are computationally quite expensive for
the same purpose.
