LAUSR

Abstract Time-dependent density functional (TDDFT) theory has become a popular method to calculate electronic excited states. The electronic circular dichroism (ECD) spectra of chiral molecules can be computed by TDDFT to resolve their absolute configurations. In this work, we evaluated the performance of TDDFT to calculate ECD of three chiral molecules whose vibronic CD spectra in a supersonic jet were recently reported. We tested seven different functionals (PBEPBE, PBE1PBE, B3LYP, mPW1PW91, M06-2X, CAM-B3LYP, and ωB97X-D) with different levels of the Pople basis set to predict the rotatory strengths of both vertical and adiabatic excitations of the chiral molecules. The 6-311++G(d,p) basis set is appropriate for the ECD calculation, and the augmentation of the diffuse function improves the quality of basis set in calculating the rotatory strength. The simulations of vibronic CD spectra under the adiabatic Hessian scheme in Cartesian coordinates have been feasible only with the M06-2X, CAM-B3LYP, and ωB97X-D functionals. The rotatory strength signs for the 0–0 transition of (1R, 2S)-ephedrine and (S)-2-amino-1-phenylethanol agree well with the experimental results. For the (1S, 2S)-pseudoephedrine conformers, the rotatory strength signs predicted using those three functionals are consistent with each other but do not coincide with the experimental results. The PBEPBE and B3LYP functionals are not robust for geometry optimizations in TDDFT because the calculations using these functionals do not provide reasonable equilibrium geometries for some conformers in the S1 state. Comparison with the conformation-specific CD spectra provides the unambiguous assessment of the DFT functionals suitable for ECD calculations.