Instability of a system and its estimation in terms of the hybrid density functional theory method: a magnetic effective density functional (MEDF) approach

Potential curves and high and low spin energy gaps for radical clusters were calculated by spin polarized molecular orbital methods. Through-space effective exchange integrals (J _ab) and relative energies of spin projected low spin states by post-Hartree-Fock (HF) calculation were reproduced by the hybrid density functional theory (DFT) method. The hybrid parameters that could reproduce post-HF values such as UCCSD(T)'s for each model had close relations with the instabilities of those systems. Information entropy and related chemical indices were used to estimate the magnitude of the instabilities. A magnetic effective density functional (MEDF) scheme for spin clusters was proposed for practical computation of J _ab values in molecular magnetic materials.