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 1 Σ + θ and 3 Σ + u states being about 0.3 eV from the exact result. Good results are obtained for H + 3 , H 3 and H ‐ 3 , too. Applications to He + 2 and He 2+ 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 X α 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 X α method and provides a simple and useful method for applications within a broad range, such as calculations on molecules and chemisorption systems.