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

Mariela M Nolasco,Catarina F Araujo,Paulo Ribeiro-Claro,Pedro D Vaz,Ana M Amado

doi:10.3390/molecules25061374

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.

Highlights

The use of periodic density functional calculations to address the vibrational spectra of molecular crystals is becoming increasingly popular [1,2,3,4,5,6,7,8,9,10,11,12]
The present work is a simple exercise that illustrates the capabilities of periodic density functional theory (DFT) as an aid in the vibrational assignment of organic crystals
Despite being more resource intensive than its discrete counterparts, the effort of running periodic DFT calculations pays off by delivering accurate estimated spectra, which can be used as a direct guide for assignments

Summary

Introduction

The use of periodic density functional calculations (periodic DFT) to address the vibrational spectra of molecular crystals is becoming increasingly popular [1,2,3,4,5,6,7,8,9,10,11,12]. The periodic DFT approach, originally developed to deal with extended inorganic systems, was found to be highly efficient in predicting the vibrational spectra of molecular crystals [13]. Periodic methods—available through programs such as VASP [14], CRYSTAL [15,16] and CASTEP [17]—are often used to assist vibrational assignments of infrared and inelastic neutron scattering (INS) spectra of molecular crystals [1,2,6,7,8,9,18].

Molecular

Representation

Comparison of Vthere

Materials and Methods

Conclusions