Calculation of electronic circular dichroism spectra with time-dependent double-hybrid density functional theory.

Time-dependent double-hybrid density functional theory is applied to the calculation of the electronic circular dichroism (CD) spectra of molecules. The TD-B2PLYP method is based on vertical excitation energies obtained from its hybrid-GGA part B2LYP in a conventional TD-DFT linear response treatment and a CIS(D) type perturbation correction for these excited states. A new benchmark set of six representative organic molecules with a wide variety of different electronic character is introduced for this investigation. The simulated TD-B2PLYP spectra are compared to experiment and those computed with the TD-B2LYP (i.e., no CIS(D) correction) and TD-B3LYP methods. Vertical excitation energies at the perturbatively corrected level are, in the majority of cases, more accurate than, e.g., with TD-B3LYP. Relative band positions are also reproduced better. In one example, the high-energy CD bands are not computed with sufficient accuracy, which is attributed to an instability of the perturbation correction. Due to the inclusion of a large portion of "exact" exchange (53%) in B2PLYP, the spectra feature less artificially created excited states and CD bands than with TD-B3LYP. In all six examined cases, TD-B2PLYP gives qualitatively correct spectra, whereas the hybrid functionals sometimes show a more erratic behavior. Therefore, we can recommend the use of the new double-hybrid approach for the computation of CD and the prediction of absolute configurations of chiral molecules.