Optimized effective-potential calculations of Ge and GaAs

How Interatomic Steps in the Exact Kohn-Sham Potential Relate to Derivative Discontinuities of the Energy

Accurate density functional calculations hinge on reliable approximations to the unknown exchange-correlation (xc) potential. The most popular approximations usually lack features of the exact xc potential that are important for an accurate prediction of the fundamental gap and the distribution of charge in complex systems. Two principal features in this regard are the spatially uniform shift in the potential, as the number of electrons infinitesimally surpasses an integer, and the spatial steps that form, for example, between the atoms of stretched molecules. Although both aforementioned concepts are well known, the exact relationship between them remained unclear. Here we establish this relationship via an analytical derivation. We support our result by numerically solving the many-electron Schrödinger equation to extract the exact Kohn-Sham potential and directly observe its features. Spatial steps in the exact xc potential of a full configuration-interaction (FCI) calculation of a molecule are presented in three dimensions.

Metal-semiconductor nanocontacts: silicon nanowires

Silicon nanowires assembled from clusters or etched from the bulk, connected to aluminum electrodes and passivated, are studied with large-scale local-density-functional simulations. Short ( approximately 0.6 nm) wires are fully metallized by metal-induced gap states resulting in finite conductance ( approximately e(2)/h). For longer wires ( approximately 2.5 nm) nanoscale Schottky barriers develop with heights larger than the corresponding bulk value by 40% to 90%. Electric transport requires doping dependent gate voltages with the conductance spectra exhibiting interference resonances due to scattering of ballistic channels by the contacts.