Vibrational Dynamics of Crystalline 4-Phenylbenzaldehyde from INS Spectra and Periodic DFT Calculations

Abstract

The present work emphasizes the value of periodic density functional theory (DFT) calculations in the assessment of the vibrational spectra of molecular crystals. Periodic calculations provide a nearly one-to-one match between the calculated and observed bands in the inelastic neutron scattering (INS) spectrum of crystalline 4-phenylbenzaldehyde, thus validating their assignment and correcting previous reports based on single molecule calculations. The calculations allow the unambiguous assignment of the phenyl torsional mode at ca. 118–128 cm−1, from which a phenyl torsional barrier of ca. 4000 cm−1 is derived, and the identification of the collective mode involving the antitranslational motion of CH···O bonded pairs, a hallmark vibrational mode of systems where C-H···O contacts are an important feature.

New Insights on the Vibrational Dynamics of 2-Methoxy-, 4-Methoxy- and 4-Ethoxy-Benzaldehyde from INS Spectra and Periodic DFT Calculations

“…But can it be assumed as the real structure, with a good level of confidence? As noted elsewhere [ 4 , 10 ], a good match between experimental and calculated spectra INS provides straightforward validation of the model. This is particularly important for the low wavenumber region—where the external modes dominate and, thus, the sensibility to crystal packing is higher.…”

“…In the last years, there has been an increasing number of reports assessing the structure and dynamics of molecular crystals based on the synergistic combination of inelastic neutron scattering (INS) spectra with periodic density functional (DFT) calculations (e.g., [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]). In INS, there are no selection rules and band intensities are proportional to the nuclei scattering cross-section and atomic displacements in the vibrational mode, both of which are large for hydrogen atoms.…”

“…On the other hand, DFT calculations—either periodic or discrete—are highly efficient in predicting the eigenvectors (atomic displacements) for the vibrational normal modes, all that is required to simulate the corresponding INS spectrum. The combined use of INS spectroscopy and periodic DFT calculations has been reported by us for several systems, including vegetable and bacterial cellulose [ 1 ], furandicarboxylate-based polymer [ 2 ], and benzaldehyde derivatives [ 4 , 9 ].…”

Vibrational Dynamics in crystalline 4-(dimethylamino) benzaldehyde: Inelastic Neutron Scattering and Periodic DFT Study

“…The power of INS to study condensed systems is strongly and accurately complemented by the use of periodic density functional theory (periodic DFT) calculations in a cooperative fashion [1][2][3][4][5][6][7][8][9][10]. DFT methods, whether discrete or periodic, offer extreme and valuable assistance by predicting vibrational normal-mode eigenvectors.…”

Molecular Structure Modulated Trap Distribution and Carrier Migration in Fluorinated Epoxy Resin

“…The common theory is quantum theory, and quantum chemical calculation is used to show the structure of the molecules and the interaction between the molecules, helping to predict the electron behavior and figure out the material properties and their internal relationship with the structure. With the development of the framework and numerical methods, the density functional theory (DFT) has become a powerful research tool, for exploring the structural and the transport properties of the polymer material considering the effects of different electric fields [29][30][31][32][33]. However, the physical mechanism of fluorination modulated surface charge behaviors hasn't been revealed from the point of molecular orbital view.…”