Electric multipole interactions in the solid phases of the hydrogen halides

The ferroelectric and proposed paraelectric phases of the hydrogen halides have been studied using a lattice of molecules which are represented by a set of electric multipoles. This model shows the dominance of quadrupole–quadrupole interactions and the importance of other multipole interactions which affect the librational motions of these molecular crystals. A dynamic ferroelectric phase model was used to calculate the frequencies of the four librational modes.