Optically-active Vibrations and Elastic Constants of Calcite and Aragonite

Treatments of the normal coordinate and the elastic constant were undertaken for two calcium carbonate crystals. By the use of the least-squares technique, we obtained sets of the force constants which reproduce satisfactorily both the observed vibrational frequencies and the macroscopic elastic constants. The intermolecular interactions, the elastic strains of the internal coordinates, and the nature of the splitting of the normal frequencies in these crystals were briefly discussed.