Resonance Raman spectra of ortho-nitrophenol calculated by real-time time-dependent density functional theory

Abstract

A new approach for the calculation of resonance Raman spectra is presented. The new method is based on dynamic polarizabilities from real-time time-dependent density functional theory, and its estimations are compared to two established techniques for the prediction of resonance Raman spectra. These established methods either use dynamic polarizabilities from linear-response time-dependent density functional theory or employ excited-state gradients. The three different ways to calculate resonance Raman spectra are investigated using the example of ortho-nitrophenol. The three methods give very similar results, respectively, for the four different exchange-correlation functionals applied. Thus, the new approach is validated for the calculation of resonance Raman intensities and advantages as well as disadvantages are discussed.

Efficient calculation of (resonance) Raman spectra and excitation profiles with real-time propagation

“…In the regime of validity of perturbation theory, thus the RT polarizability method and the PT polarizability method are expected to yield very similar results. This was indeed observed by Thomas et al 43 In fact, for a weak δ-pulse perturbation [see Eq. 29], the RT polarizability method can be shown to correspond to the PT polarizability method as follows: The linear response formula (A6) can be used directly to calculate the time-dependent expectation value of the electric dipole moment to first order, under the assumption that κ β is sufficiently small…”

“…II. Thomas et al observed a good agreement between the two methods for ortho-nitrophenol 43 as well.…”

“…Instead of using PT-TDDFT for the excited state gradient approximation, as is routinely done, 43,54 the latter can also be performed in an RT-TDDFT framework: In order to do so, a very fine frequency resolution of the Fourier transform [see Eq. (27)] is required, which is usually not achieved by the fast Fourier transform (FFT) algorithm due to computational limits (the resolution is ∝ 1 ∆tN steps ; i.e., at a time step of ∆t = 0.1 a.u., a resolution of 0.0001 eV would require roughly 30 000 000 steps).…”

“…Its application to RRS involves a Placzek type expansion 40 of the electronic polarizability tensor around the equilibrium geometry. 36 Besides calculations of surface-enhanced Raman spectra via RT-TDDFT, 41,42 Thomas et al 43 have applied the calculation of the electronic polarizability in an RT-TDDFT framework to RRS, also by applying a Placzek type expansion. They compared their results to both Jensen's polarizability method and the excited state gradient method 44 in a PT-TDDFT framework finding a good agreement of the resulting RRS spectra.…”

Distinguishing chemical and electromagnetic enhancement in surface‐enhanced Raman spectra: The case of para‐nitrothiophenol

“…Nevertheless, the comparison shows that the RT‐TDDFT method is generally able to correctly estimate the Raman spectrum of pNTP. Since the chemical enhancement relies on the resonance with charge‐transfer transitions between the molecule and the metallic nanostructure, it is important to note that the RT‐TDDFT method can also be used to predict resonance Raman spectra as we have shown in reference …”