A THEORY OF MELTING OF MOLECULAR-CRYSTALS .2. PHASE-DIAGRAMS AND RELATIONS WITH SOLID-STATE TRANSITIONS

The Pople and Karasz theory of melting of molecular crystals is extend ed to include the third energy parameter mentioned in our previous pap er.(1) The modified form of the Pople and Karasz theory is used to stu dy solid-solid transitions and to obtain complete phase diagrams for t ransitions under pressure. It is found that solid-solid and melting tr ansitions become second-order under certain conditions. The entropy of melting as a function of the ratio of the solid transition to boiling temperature, the theoretical phase diagrams as well as the melting en tropy versus the solid transition entropy are compared with available experimental data and as well as the Pople and Karasz theory.