Failure of time-dependent density functional theory for excited state surfaces in case of homolytic bond dissociation

Adiabatic time-dependent density functional theory (ATDDFT) has much too low excitation energies at long bond length in (dissociating) electron pair bonds. This easily escapes attention partly due to the occurrence of the problems at slightly longer distances than the equilibrium geometry, and partly due to fortuitous error cancellation between wrong (too high) DFT ground state energies being added to wrong (too low) ATDDFT excitation energies to obtain the excited state E vs. R curves. © 2008 Elsevier B.V. All rights reserved.