Dynamical Correlated-Effective-Field Approximation

The correlated-effective-field (CEF) approximation originally proposed by Lines is improved by introducing a self-consistency equation which is constructed from the transverse dynamical susceptibility (dynamical CEF approximation). This approximation preserves the conceptual simplicity of the molecular-field approximation and can be applied to complicated magnetic systems such as orbitally unquenched magnetic compounds. For orbitally quenched isotropic Heisenberg systems this dynamical CEF approximation is equivalent to the RPA-Green's function method in both the paramagnetic and ordered states.