Application of the Cluster Variation Method to the sd Interaction Hamiltonian
Abstract
The groundstate energy of an sd interacting system is calculated through the cluster variation technique. This method has been slightly reformulated so that only the expectation values of the problem appear as unknowns. In order to treat the sd exchange Hamiltonian without decoupling, up to threeparticle density matrices are retained in the entropy expansion. Minimization of the free energy leads to equations that can be solved for the expectation values at zero temperature. The groundstate energy lowering is calculated to be W_{0}=2N(0)D^{2} exp[4N3μJN(0)], where μ=1 for antiferromagnetic coupling (J<0), and μ=13 for ferromagnetic coupling (J>0).
 Publication:

Physical Review
 Pub Date:
 November 1968
 DOI:
 10.1103/PhysRev.175.680
 Bibcode:
 1968PhRv..175..680H