The accurate determination of excited-state absorption (ESA) is central to screening for optical limiting materials, corroborating experimental transient absorption spectra, and the determination of several other higher order, non-linear responses to external fields. Benchmarking of a recently proposed real time time-dependent density functional theory (RT-TDDFT) method for calculating ESA was performed upon eight organic chromophores using two GGA (BLYP, PBE), five hybrid GGA (B3LYP, CAM-B3LYP, PBE0, BHandH, BHLYP), and one hybrid meta-GGA (M06) functionals and two basis sets (6-31G*, cc-pVDZ). The method used involves the real time propagation of excited state densities (obtained from linear response TDDFT (LR-TDDFT) gradient calculations) that have been perturbed by electric field delta pulses. The densities are propagated using a second-order Magnus propagator, and the oscillating dipoles are dampened over time to produce absorption spectra with homogeneous broadening. The propagation of excited state densities was performed with ground state functionals, resulting in a non-stationary reference. To approximately account for this reference, the dynamic dipole of the excited state density without electric field perturbation is subtracted from the dipoles of the simulations which included the delta pulses. The Fourier transform of these dipole changes then affords the full ESA. This method is compared to quadratic response TDDFT (QR-TDDFT), which can calculate ESA from transition dipole moments between LR-TDDFT excited states. Discrete QR-TDDFT excitations for the same set of dyes were calculated with BLYP, B3LYP, CAM-B3LYP, BHLYP, and BHandH using the same basis sets. ESA spectra were simulated by convoluting the QR stick spectra with a Lorentzian lineshape with half width at half maximum of 0.12 eV. Benchmarking has provided that LR/RT-TDDFT is consistent across basis sets and is blueshifted linearly dependent on percentage of exact exchange in the functional used with the dependence different for different peaks. Additionally, QR-TDDFT calculations, when spectra were normalized by absorbance, were in qualitative agreement with LR/RT-TDDFT despite a redshift of about 1-2 eV. The RT-TDDFT method is able to offer an alternative to QR-TDDFT for generating ESA with the added benefit of affording a complete spectrum.

Benchmarking excited state absorption via LR/RT-TDDFT for a series of organic chromophores

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.