Spin Symmetry Requirements in Density Functional Theory: The Proper Way to Predict Magnetic Coupling Constants in Molecules and Solids

Abstract

Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Abstract In this paper it is argued that the use of density functional theory (DFT) to solve the exact, non-relativistic, many-electron problem, for magnetic systems requires imposing space and spin symmetry constraints exactly in the same way as it is currently done in ab initio wave function theory. This strong statement is supported on pertinent calculations for selected systems representative of organic diradicals, molecular magnets and antiferromagnetic solids. These calculations include several wave function methods of increasing accuracy and different forms of the exchangecorrelation functional. The comparisons of numerical results carried out always within the same standard Gaussian Type Orbital atomic basis set show that imposing or not the spin and space constraints (restricted or unrestricted formalisms) leads to contradictory results. Therefore, it appears that, in the case of the Heisenberg magnetic constant, the present exchange-correlation functionals may provide reasonable numerical results although for the wrong physical reasons thus evidencing the failure of the current DFT methods to properly describe magnetic systems.

Spin in density‐functional theory

“…This is indicated by the superscript ' '(ss).' ' The multiplet-DFT scheme of Daul [117,118] and the restricted open-shell KS (ROKS) scheme [119][120][121][122][123][124] as well as related approaches [125,126] proceed along these lines, but usually include additional ideas originating from Hartree-Fock theory. [127,128] It appears that if applied in a spin-restricted formalism, all available approximate exchange-correlation functionals have to be understood as approximations to E ðssÞ xc [q, Q] and not as approximations to E xc [q, Q].…”

[CpNi(diselenolene)] Neutral Radical Complexes: Electron Paramagnetic Resonance and Density Functional Theory Investigations

“…Although this DFT-BS method has been criticized, 35 it enables us to calculate our rather large system, (bds)NiCp‚‚‚CpNi(bds) without having to approximate it to a simpler model. First, the value of J has been calculated for the idealized dimer shown in Figure 4.…”

Restricted Ensemble-Referenced Kohn−Sham versus Broken Symmetry Approaches in Density Functional Theory: Magnetic Coupling in Cu Binuclear Complexes

“…In the present work, we extend our previous studies about the REKS description of magnetic systems 34,35 to a new series of large Cu binuclear complexes, which cover a broad range of physical situations, from strongly antiferromagnetic coupling to ferromagnetic interactions. In doing so one must be aware of the strong dependence of the magnitude of the calculated magnetic interaction on the exchange-correlation functional employed in the calculations.…”