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

Abstract

We investigate approaches for the calculation of (resonance) Raman spectra in a real-time time-dependent density functional theory (RT-TDDFT) framework. Several short time approximations to the Kramers, Heisenberg, and Dirac polarizability tensor are examined with regard to the calculation of resonance Raman spectra: One relies on a Placzek type expansion of the electronic polarizability and the other one relies on the excited state gradient method. The first one is shown to be in agreement with an approach based on perturbation theory in the case of a weak-pulse perturbation. The latter is newly applied in a real time propagation framework, enabled by the use of Padé approximants to the Fourier transform which allow for a sufficient resolution in the frequency domain. An analysis of the performance of Padé approximants is given. All approaches were found to be in good agreement for uracil and R-methyloxirane. Moreover it is shown how RT-TDDFT can be used to calculate Raman excitation profiles efficiently.

Vibrational (resonance) Raman optical activity with real time time dependent density functional theory

“…It is also applicable within a RT-TDDFT framework for the calculation of Raman spectra 65,93 giving identical results as the LR-TDDFT approach for a weak perturbation. The Raman and ROA intensities for each normal mode p within these STAs and the harmonic approximation are then given by…”

“…An investigation off the dependence of the spectrum on the amount of simulation time was given in Ref. 65.…”

“…Vibrational spectra in the STA were calculated according to the numerical scheme as in previous works. 65,93 In all calculations, we used the PBE exchange-correlation functional 110 and either the aug-QZV2P-GTH basis set 111 or the TZVP-GTH basis set 111 in combination with GTH pseudopotentials. 112 The Journal of Chemical Physics…”

“…63 The description of the dynamics in the time domain allows us to obtain all excited states from just one simulation run, without losing information about the individual transitions, 64 and works well also for a high density of states, which was demonstrated for a (resonance) Raman excitation profile. 65 Aside from that, pseudopotentials 66,67 may be used in order to describe chemically inert core electrons, which again reduces the computational resources needed for the calculation of ROA spectra and was recently implemented in CP2K [68][69][70] using density functional perturbation theory (DFPT) for static and dynamic 32 ROA calculations as well as their analysis in terms of localized molecular orbitals. 71 A well known issue connected with the description of electromagnetic response properties such as electronic circular dichroism (ECD) and ROA is that calculations of the response properties show a dependence on the choice of the coordinate system, due to the inevitably finite basis sets in practical calculations.…”

Recent Trends in Chiroptical Spectroscopy: Theory and Applications of Vibrational Circular Dichroism and Raman Optical Activity

“…More complicated resonance Raman and ROA phenomena involving many electronic states are difficult to simulate. Time‐dependent AIMD‐based simulations seem to be extremely useful for these cases …”