Real-space density-functional calculations for transport properties of nanostructures

Electronic devices have advanced at an amazing rate over the last decade, and at the heart of these advances has been the technology of nanoscale devices. In this review, we will introduce an efficient and highly accurate calculation method that can provide first-principles electronic structures as well as electron transport properties for nanostructures attached to truly semi-infinite crystalline electrodes on both sides. This method is formulated by the real-space finite-difference method within the framework of density-functional theory. The real-space finite-difference method does not suffer from the artificial periodicity problems that arise in the method using plane-wave basis sets or linear-dependence problems that occur in the methods using atomic basis sets. We will illustrate applications of first-principles electron transport calculations to a variety of systems ranging from atomic and molecule wires to the tip-and-surface system in a scanning tunneling microscope, which contains about a hundred atoms.