DYNAMIC SPIN SUSCEPTIBILITY IN THE HUBBARD-MODEL

The dynamic spin susceptibility in the Hubbard model is calculated on the basis of the new diagram technique developed for systems with stro ng correlation. In the leading-order approximation, the single-site in teraction is allowed and electron hopping is taken into account using the evolution operator. The second order of perturbation theory is con sidered and the sum of 1PI two-particle single-site diagrams of the la dder type is calculated. The equations for calculating the static susc eptibility and the spin wave spectrum are obtained.