Chemical binding in small molecules by the spin-density-functional formalism

A brief review is given of some results within the spin-density-functional (SDF) formalism. The local-spin-density (LSD) approximation, that is, the approximation which is formally exact in the limit of slow and weak spatial variations, gives results of a useful accuracy for valence electrons in atoms and solids, and the accuracy for molecules may be illustrated by the hydrogen-molecule energy curves in the lowest 1Σ+θ and 3Σ+u states being about 0.3 eV from the exact result. Good results are obtained for H+3, H3 and H-3, too. Applications to He+2 and He2+2 inform about the range of applicability of the approximation. Further, the new numerical method developed for these molecular applications allows an evaluation of the multiple-scattering Xα method, showing shortcomings of both the potential and the multiple-scattering approach used in this method. We argue that the SDF formalism within the LSD approximation is physically superior to the Xα method and provides a simple and useful method for applications within a broad range, such as calculations on molecules and chemisorption systems.