Structural and conducting properties of metal carbon-nanotube contacts: Extended molecule approximation

The structural and conducting properties of single-wall carbon nanotubes (SWCNs) in embedded as well as in side contact with metal leads are obtained using efficient formalisms based on spin polarized tight-binding formulation incorporating full consideration of $s$, $p$, and $d$ basis sets for carbon and metal atoms. The full structural relaxation of the combined SWCN and metal system is found to be essential for realistic characterization of conductivity. More importantly, convergence with respect to the number of the metal-lead (ML) atoms in contact with the SWCN is found to be even more critical. Our results indicate that in order to maximize device efficiency, one needs to use ML-SWCN systems with a minimal ML-SWCN contact width to SWCN length ratio. If this ratio is large enough, the SWCN cannot be seen independently of its contacts and the ML-SWCN-ML system behaves as a molecular wire. Additionally, the ML-SWCN-ML complex is found to have spin-selective transport properties for certain bias range, making it a promising candidate for use as a spin valve in nanoelectronic devices.