In this study, we compute the hyperpolarizability of the nitroaniline isomers, para-nitroaniline (pNA), ortho-nitroaniline (oNA), and meta-nitroaniline (mNA), by density functional theory (DFT), including with optimally tuned range separated hybrid (RSH) functionals. By utilizing the nitroanilines hyperpolarizability trend based on charge transfer (pNA>oNA>mNA), we can uncover how the excitation wavelength affects the prediction of the hyperpolarizabilities in both on and off resonant regimes, and optimal gap tuning of RSH functionals. In non-resonant regions, with reference to CCSD/aug-cc-pVDZ and experimental studies, we find that some computational approaches do not always reproduce the nitroanilines trend at specific excitation wavelengths. For example, RSH functionals require optimal gap tuning to reproduce the trend. In resonant regions, we find that the damped response theory predicts that the trend is maintained at the two-photon absorption, however, it breaks near the one photon pole. This suggests that the underlying charge transfer characteristics are undermined in the one-photon pole which in comparison to the two-state model suggests that this is due to the presence of other electronic states in some of the isomers. Furthermore, we find that cases where optimal gap tuning is ineffective (pathological behavior) are dependent on the excitation wavelength.
Supplementary material for Influence of the Excitation Wavelength on First Order Hyperpolarizabilities and Optimal Gap Tuning of Range Separated Hybrid Functionals
Plots of the absolute differences against the range separation parameter used to determine the optimized \omega values, previous experimental studies of hyperpolarizabilities were done on nitroaniline isomers, variation of the hyperpolarizability from the static limit to 2000 nm for the tuned RSH functionals, results from TDDFT computations, comparison of the damped response theory to the damped two state model, variation of the hyperpolarizabilities of pNA and mNA with respect to the range separation parameter for RSH functionals at the static limit, 1064 nm, and 1907 nm in the vacuum; and coordinates of the computed ground state geometries of all the nitroaniline isomers.