A Perspective on the Relative Merits of Time-Dependent and Time-Independent Density Functional Theory in Studies of the Electron Spectra Due to Transition Metal Complexes. An Illustration Through Applications to Copper Tetrachloride and Plastocyanin

Evaluation of the excitation energies in CuCl42- and plastocyanin was carried out with three different density functional theory (DFT) methods: time-dependent DFT (TDDFT), Delta DFT, and Delta self consistent field (SCF)-DFT. Use was made of two local (local density approximation and BP86), two hybrid (B3LYP and PBE0), and one long-range corrected (LC-BP86) functionals to probe the effect of the exact exchange on the excitation energies. Some well-known deficiencies observed in TDDFT were explained on the basis of lacking orbital relaxation and two-electron terms not considered in adiabatic TDDFT. Delta self consistent field (SCF)-DFT reproduces well the position of the charge-transfer excitations and yields results in best agreement with experiment regardless of the system or functional used. We conclude that the orbital relaxation and proper account of higher-order terms neglected in adiabatic TDDFT are of great importance for the simulation of excitation spectra. (C) 2014 Wiley Periodicals, Inc.