$O\left(N\right)\mathrm{}$ real-space method for ab initio quantum transport calculations: Application to carbon nanotube–metal contacts

We present an ab initio $O\left(N\right)\mathrm{}$ method that combines an accurate optimized-orbital solution of the electronic structure problem with an efficient Green’s function technique for evaluating the quantum conductance. As an important illustrative example, we investigate carbon nanotube–metal contacts and explain the anomalously large contact resistance observed in nanotube devices as due to the spatial separation of their conductance eigenchannels. The results for various contact geometries and strategies for improving device performance are discussed.