Chiral Crystal Packing Induces Enhancement of Vibrational Circular Dichroism

We demonstrate that molecular vibrations with originally low or zero intensity in a vibrational circular dichroism (VCD) spectrum attain chirality in molecular crystals by coordinated motion of the atoms. Ab initio molecular dynamics simulations of anharmonic solid‐state VCD spectra of l ‐alanine crystals reveal how coherent vibrational modes exploit the space group's chirality, leading to non‐local, enhanced VCD features, most significantly in the carbonyl region of the spectrum. The VCD‐enhanced signal is ascribed to a helical arrangement of the oscillators in the crystal layers. No structural irregularities need to be considered to explain the amplification, but a crucial point lies in the polarization of charge, which requires an accurate description of the electronic structure. Delivering a quantitative atomic conception of supramolecular chirality induction, our ab initio scheme is applicable well beyond molecular crystals, for example, to address VCD in proteins and related compounds.