N. H. List, J. M. H. Olsen, T. Rocha-Rinza, O. Christiansen, J. Kongsted
Understanding and rationalization of the optical properties of fluorescent proteins are of great importance for life sciences due to their numerous applications as fluorescent biomarkers. Time-dependent density functional theory (TD-DFT) is a computationally appealing approach to accomplish this task. We present an evaluation of the performance of commonly used XC-functionals for the prediction of excitation energies of GFP-like chromophores. In particular, we have considered the TD-DFT vertical excitation energies of chromophores displaying different charge states. We compare the quality of six XC-functionals, belonging to the GGA, hybrid and Coulomb-attenuated classes of XC-functionals, by comparison with RI-CC2 results. We find that none of the tested XC-functionals are capable of providing a simultaneous good description of all charge states and, interestingly, the hybrid functionals are found to give the overall best performance. The Coulomb-attenuated CAM-B3LYP functional systematically overestimates the excitation energies of the charged states; however, its error has the attractive feature of being size-independent and almost identical for the considered anionic and cationic systems. Finally, we have explored the possibility of optimizing the attenuation parameter to yield overall excitation energies in good agreement with RI-CC2 results. On the basis of these predictions, however, there does not appear to be a common attenuation parameter minimizing the deviation for every charge state. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011.