Instability of the paramagnetic state in the kinematic field approximation in the Hubbard model

Within the scope of the approximation of a kinematic field I have been calculating the uniform paramagnetic susceptibility χ(0,0)=δR(H)/δH when H → 0 and U → ∞. It turns out that χ(0,0) < 0 in the all region, where R=0 (i.e. 0,7 > or approx. n ≥ 0). (author). 6 refs, 1 fig