To test if the observed vibrational shifts are due to co-crystallization of HCN and ethane, we have screened 9760 co-crystal candidates using dispersion-corrected Density Functional Theory (DFT) calculations coupled to a particle-swarmbased crystal structure prediction algorithm. Our stability estimates for the lowest energy candidates account quantum mechanically for electronic effects such as polarization of neighboring molecules, explicit treatment of vdW/dispersion effects (we rely on the vdW-DF2 (29) functional) and vibrational contributions to enthalpy and entropy, as well as a negligible pressure-volume, Δ(pV), term (Fig. ).