Quantum‐chemical derivation of electro‐optical parameters for alkanes

Abstract

An approach for deriving the bond electro-optical parameters (EOPs) of the bond polarizability model (BPM) from quantum-chemical calculations is proposed. The approach was used to obtain the equilibrium and valence EOPs for the CH and CC bonds in saturated hydrocarbons from the results of the DFT calculations of small chain alkanes. The parameters derived are in the range of those found in the literature. The results of the study show that for this class of molecules the polarizability tensor can be constructed as the sum of the individual bond polarizability tensors thus indicating the validity of the BPM. The use of the parameters in the calculation of the Raman activity of the normal modes of 2-methylbutane shows a good correlation between the data obtained in the DFT calculations and those with the BPM. Factors influencing the reliability and transferability of the parameters are discussed.

Unbranched n-Alkanes

“…This is why the triple zeta basis set used here was augmented with diffuse and polarization function on both, heavy and light atoms (indicated by ++ and **, respectively). Beside the fair prediction of absolute intensities, it should be noted that the overall polarizability of alkanes is well described by additive bond polarizabilities [69,70], which suggests that relative intensities of different conformers predicted by the B3LYP approach might involve an uncertainty of less then 20 %. The strong predictive power of B3LYP regarding relative Raman intensities was recently demonstrated by Zvereva et al [67].…”

Predicting Raman Spectra of Condensed Polymer Phases from MD Simulations

“…Each contribution depends upon the bond type, orientation, and length. Bond polarizability models have been widely employed to represent the polarizability of single molecules, polymers, silica glasses, and nanotubes. ,,, For polymeric materials, only a few studies have focused on computing the Raman spectra of crystals and uses rather small molecular systems …”

“…It assumes the polarizability of a molecule is the sum of independent contributions from its chemical bonds. The bond polarizability constants are sometimes called electro-optical parameters in literature. − Values for bond polarizability constants can be obtained either by fitting to experimental Raman peak intensities of molecules containing the bonds of interest or by fitting molecular polarizabilities computed using DFT . The bond polarizability model has been used successfully to represent the molecular polarizability of hydrocarbons, ,,, small molecules, and silica polymorphs. , In our work, we will use the bond polarizability model to compute the Raman-activity of molecular vibrations in condensed phases.…”

Calculation of off‐resonance Raman scattering intensities with parametric models

“…This approach was applied for a test on alkanes for which, as already discussed, a wealth of experimental data is available. [67] In that work, seven n-alkanes provide a database consisting of 34 equilibrium nonzero polarizability tensor components, and 55 CH bonds and 47 CC bonds polarizability derivatives obtained by stretching separately all different individual bonds. Assuming the identity of all CH and of all CC bonds, the 12 EOPs can thus be determined with a reliable statistics from 136 values in the database.…”

“…Recently, an approach similar to the derivation of parameters for the alkanes [67] was employed to obtain a set of EOPs permitting the calculation of the Raman spectra of polypeptides. [71] The strategy was however modified by comparison with the work about alkanes discussed above.…”