Spin correlation functions by generalized spin orbital density functional and multireference approaches

We presented the comparative study of spin correlation functions of generalized spin orbital density functional theory (GSO-DFT) and configuration interaction (CI) wave function (WF) approaches, in particular for simple models. The differences between them are ascribed to that of their symmetry frameworks, which is similar to that between the Heisenberg (HB) model and its mean-field approximation. Therefore, the prescriptions to spin-frustrated and -degenerated systems are examined from the viewpoint of the HB model and its solutions. Both nondynamic electron correlation and spin-dependent interactions are found to be important in the surface crossing regions. The GSO complete-active-space (CAS) Cl and CAS self-consistent field (SCF) are also discussed as the multireference approaches for the systems. (C) 2003 Wiley Periodicals, Inc.