Análise das propriedades estruturais, eletrônicas e ópticas dos cristais dos principais ácidos graxos da manteiga de cacau (palmítico, esteárico, oleico e linoleico) calculadas usando a teoria do funcional da densidade

Abstract

Density Functional Theory (DFT) calculations were performed on four fatty acid crystals found in chocolate, revealing distinct electronic and optical properties. Time Dependent DFT (TD-DFT) calculations of the UV/Vis absorption spectra showed that saturated fatty acids, palmitic and stearic, exhibit similar absorption patterns. In contrast, the unsaturated fatty acids, oleic and linoleic, display unique spectral characteristics due to their C=C double bonds. Analysis of the electronic density of states indicated that oleic and linoleic acids have smaller HOMO-LUMO gaps compared to their saturated counterparts. The DFT calculations, employing the GGA PBE functional with dispersion correction, demonstrated strong agreement with experimental X-ray diffraction data for lattice parameters and hydrogen-bond lengths. Band structure analysis revealed that palmitic and stearic acids possess indirect band gaps of 5.16 eV and 5.11 eV, respectively, revealing insulating characteristics, while oleic and linoleic acids show smaller indirect band gaps of 4.35 eV and 4.18 eV, respectively. Optical absorption simulations closely matched the estimated Kohn Sham gaps, with anisotropic absorption behaviors observed across different polarization planes of incident light. These findings provide a comprehensive understanding of the electronic, structural, and optical properties of fatty acid crystals in chocolate, contributing valuable insights for potential applications.