Lattice dynamics, thermodynamic functions, and phase transitions of p‐dichloro‐ and 1,2,4,5‐tetrachlorobenzene

The thermodynamic properties and phase transitions of p‐C6H4Cl2 and 1,2,4,5‐C6H2Cl4 have been studied, using an intermolecular potential function of the atom–atom type. The Debye–Einstein approximation to the density of states is checked against the complete calculation for the case of p‐C6H4Cl2. This approximation is sufficiently accurate for the calculation of thermodynamic properties. The behavior of the free energy in the vicinity of the phase transition is studied for both crystals. The calculations are consistent with experimental data.