Theoretical Spectroscopy of Carbocyanine Dyes Made Accurate by Frozen Density Correction to Excitation Energies Obtained by TD-DFT

We present long-awaited answer to the puzzling question of why the TD-DFT fails to predict the excitation energies in polymethine dyes accurately. The density functional theory methods were suspected to be inaccurate due to self interaction error inherent in exchange-correlation potentials. Here we decisively show that it is the linear response approximation that is responsible for these inaccuracies. Next, we use frozen density to evaluate the excitation energy beyond the linear response and increase the accuracy of the predictions. This recipe uniformly improves the accuracy of the first absorption maxima prediction in cyanine homologous series to within 25 nm. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110: 3095-3100, 2010