Magnetic susceptibility, exchange interactions and spin-wave spectra in the local spin density approximation

Starting from an exact expression for the dynamical spin susceptibility in the time-dependent density functional theory, a controversial issue regarding exchange interaction parameters and spin-wave excitation spectra of itinerant electron ferromagnets is reconsidered. It is shown that the original expressions for exchange integrals based on the magnetic force theorem (Liechtenstein et al 1984 J. Phys. F: Met. Phys. 14L125) are optimal for calculations of the magnon spectrum, whereas the static response function is better described using the 'renormalized' magnetic force theorem given by Bruno (2003 Phys. Rev. Lett. 90 087205). This conclusion is confirmed by ab initio calculations for Fe and Ni.