Timedependent Gutzwiller theory of magnetic excitations in the Hubbard model
Abstract
We use a spinrotational invariant Gutzwiller energy functional to compute randomphaseapproximationlike (RPA) fluctuations on top of the Gutzwiller approximation (GA). The method can be viewed as an extension of the previously developed GA+RPA approach for the charge sector [G. Seibold and J. Lorenzana, Phys. Rev. Lett. 86, 2605 (2001)] with respect to the inclusion of the magnetic excitations. Unlike the charge case, no assumptions about the time evolution of the double occupancy are needed in this case. Interestingly, in a spinrotational invariant system, we find the correct degeneracy between triplet excitations, showing the consistency of both computations. Since no restrictions are imposed on the symmetry of the underlying saddlepoint solution, our approach is suitable for the evaluation of the magnetic susceptibility and dynamical structure factor in strongly correlated inhomogeneous systems. We present a detailed study of the quality of our approach by comparing with exact diagonalization results and show its much higher accuracy compared to the conventional HartreeFock+RPA theory. In infinite dimensions, where the GA becomes exact for the Gutzwiller variational energy, we evaluate ferromagnetic and antiferromagnetic instabilities from the transverse magnetic susceptibility. The resulting phase diagram is in complete agreement with previous variational computations.
 Publication:

Physical Review B
 Pub Date:
 April 2004
 DOI:
 10.1103/PhysRevB.69.155113
 arXiv:
 arXiv:condmat/0311128
 Bibcode:
 2004PhRvB..69o5113S
 Keywords:

 71.10.w;
 71.27.+a;
 71.45.Gm;
 Theories and models of manyelectron systems;
 Strongly correlated electron systems;
 heavy fermions;
 Exchange correlation dielectric and magnetic response functions plasmons;
 Condensed Matter  Strongly Correlated Electrons
 EPrint:
 12 pages, 8 figures