Green's function formalism for calculating spin-wave spectra

We propose a formalism for calculating ab initio spin-wave spectra which is based on the many-body temperature Green's function. The main quantity to be calculated is the linear magnetic susceptibility from which all magnetic excitations involving the creation of an additional spin in the system can formally be obtained. The Schwinger functional derivative technique is emp loyed in calculating the self-energy. The approach avoids both the assumpti on of local spins (Heisenberg model) and the use of a local exchange and co rrelation interaction (local-density approximation). Starting from the GW a pproximation we obtain a Bethe-Salpeter equation for the kernel describing the interaction between electrons in both spin channels. However, this kern el exhibits a nonlocal screened interaction. [S0163-1829(99)08933-X].