On the performance of density functional theory for symmetry-breaking problems

Density functional theory (DFT) has been applied to three open-shell molecules (NO3, O-4(+), and O-2(+)) for which the unrestricted Hartree-Fock (UHF) wavefunction breaks spatial symmetry. In contrast to Hartree-Fock, all of the standard DFT methods we employed yielded symmetric densities for each of the molecules considered. Symmetry-broken solutions were obtained with DFT only when we used hybrid functionals including unusually large fractions of Hartree-Fock exchange. The exchange functional seems more important than the correlation functional in determining whether symmetry is preserved or broken. (C) 1999 Elsevier Science B.V. All rights reserved.