Breakdown of broken-symmetry approach to exchange interaction

Abstract

Broken-symmetry (BS) approaches are widely employed to evaluate Heisenberg exchange parameters, primarily in combination with DFT calculations. For many magnetic materials, BS-DFT calculations give reasonable estimations of exchange parameters, although systematic failures have also been reported. While the latter were attributed to deficiencies of approximate exchange-correlation functional, we prove here by treating a simple model system that the broken-symmetry methodology has serious problems. Detailed analysis clarifies the intrinsic issue with the broken-symmetry treatment of low-spin states. It shows, in particular, that the error in the BS calculation of exchange parameter scales with the degree of covalency between the magnetic and the bridging orbitals. This is due to the constraint on the form of multiconfigurational state imposed by the BS determinant, a feature common to other single-reference methods too. As a possible tool to overcome this intrinsic drawback of single-determinant BS approaches, we propose their extension to a minimal multiconfigurational version.

13 pages, 5 figures

References in corpus (12)

• Maximally localized Wannier functions: Theory and applications
• Orbital physics in transition metal compounds: new trends
• Ferromagnetism in Hubbard Models
• A multiconfigurational hybrid density-functional theory
• Ferromagnetism in multi--band Hubbard models: From weak to strong Coulomb repulsion
• $ab$-$initio$ Approaches for Low-Energy Spin Hamiltonians
• Theoretical Prediction of Magnetic Exchange Coupling Constants from Broken-Symmetry Coupled Cluster Calculations
• Broken-symmetry self-consistent GW approach: degree of spin contamination and evaluation of effective exchange couplings in solid antiferromagnets
• Ferromagnetic kinetic exchange interaction in magnetic insulators
• Natural orbitals and two-particle correlators as tools for analysis of effective exchange couplings in solids
• Broken symmetry $G_0{W}_0$ approach for the evaluation of exchange coupling constants
• Ab initio Simulations of Fe-based Ferric Wheels