Low-Frequency Vibrational Spectroscopy and Crystal Structure Predictions for Fumaric Acid and Maleic Acid

Low-frequency vibrational spectroscopy of molecular crystals provides new benchmarks for validating crystal structure prediction methods based on fundamental computational chemistry simulations. The terahertz and Raman spectra of the lattice vibrations of crystalline maleic acid and fumaric acid have been measured and then successfully modeled using solid-state density functional theory to accurately account for the intermolecular forces in the crystals. This rigorous computational approach has been combined with a faster-running molecular mechanics evaluation of numerous crystal packing variations to identify previously unknown polymorphs of both compounds.