From the optimized geometries, we compute the partial Hessian of propionate with ASH numerically, using analytic gradients of the energy with respect to nuclear coordinates from B3LYP-D4. This Hessian was then weighted by the masses of the nuclei and diagonalized, yielding the vibrational normal modes. We did not project out the translational and vibrational modes, as they couple to the rest of the complex and are ill-defined for partial Hessian calculations ; however, we omit them from the following analysis. We additionally obtain the derivatives of the dipole moments along the normal modes, which provide infrared intensities.