Intensity‐Carrying Modes in Raman and Raman Optical Activity Spectroscopy

Abstract

We describe a quantum-chemical approach for the determination of modes with maximum Raman and Raman optical activity (ROA) intensity by maximizing the intensities with respect to the Raman and Raman optical activity intensity, respectively, which is shown to lead to eigenvalue equations. The intensity-carrying modes are in general hypothetical modes and do not directly correspond to a certain normal mode in the spectrum. However, they provide information about those molecular distortions leading to intense bands in the spectrum. Modes with maximum Raman intensity are presented for propane-1,3-dione, propane-1,3-dionate, and Lambda-tris(propane-1,3-dionato)cobalt(III). Moreover, the mode with highest ROA intensity is examined for this chiral cobalt complex and also for the (chiral) amino acid L-tryptophan. The Raman and ROA high-intensity modes are an optimal starting guess for intensity-tracking calculations, in which selectively normal modes with high Raman or ROA intensity are converged. We present the first Raman and ROA intensity-tracking calculations. These reveal a high potential for large molecules, for which the selective calculation of normal modes with high intensity is desirable in view of the large computational effort required for the calculation of Raman and ROA polarizability property tensors.

Raman spectra from ab initio molecular dynamics and its application to liquid S-methyloxirane

“…KS-DFT was used as the electronic structure method in the framework of the Gaussian and plane waves formalism. We tested three different density functionals: BP86, 48,49 that has been found to perform well in static frequency calculations within the doubleharmonic approximation, [50][51][52][53][54][55][56][57][58][59][60][61][62][63] 73,74 for comparing purposes. BLYP-Goedecker-Teter-Hutter (GTH) (in case of PBE the PBE-GTH) pseudopotentials [75][76][77] and the TZVP-GTH and DZVP-GTH basis sets were applied.…”

MOVIPAC: Vibrational spectroscopy with a robust meta‐program for massively parallel standard and inverse calculations

“…Therefore, an algorithm which selectively calculates only the intense bands in a spectrum is desirable. For this task, Intensity-Tracking [30][31][32][33] has been developed and implemented into the AKIRA program package. This algorithm achieves to produce a spectrum containing the important features and simultaneously saving computational time by avoiding the calculation of normal modes with small intensities.…”

“…These ICMs have been found by Torii et al [70] and in an alternative derivation by us. [31] In a similar way, the ICMs can be derived for Raman intensities where the Cartesian gradients of the electric-dipole-electric-dipole polarizability tensor are required [71,32] for the eigenvalue equation. This concept has also been extended to Raman Optical Activity (ROA) spectroscopy, where, in addition to the electric-dipole-electric-dipole polarizability tensor, the electric-dipole-magnetic-dipole and electric-dipole-electric-quadrupole polarizability tensors are necessary.…”

“…This concept has also been extended to Raman Optical Activity (ROA) spectroscopy, where, in addition to the electric-dipole-electric-dipole polarizability tensor, the electric-dipole-magnetic-dipole and electric-dipole-electric-quadrupole polarizability tensors are necessary. [32] Intensity-Tracking using these ICMs has been implemented for IR, Raman, and ROA spectra. [31,32] IR, Raman, and ROA spectra contain, in contrast with Resonance Raman spectra, usually many intense bands which may lead to a slow convergence of Intensity-Tracking calculations.…”

“…[29] Also, AKIRA has been continuously developed and supplemented by new algorithms like Intensity-Tracking. [30][31][32][33] Other offsprings are the anharmonicity program ANF [14] and the resonance Raman program KKTRANS. [34] Here, we present the latest developments of SNF and AKIRA which are now united into one single program package for vibrational spectroscopy called MOVIPAC.…”