Calculation of the free energies for the solid phases of ammonium halides

Abstract

Using mean field theory, we calculate the free energies of the solid phases of ammonium halides. The temperature and pressure dependences of the free energies are obtained using experimental phase diagrams of the ammonium halides. From these dependences, we calculate numerically the specific heat as a function of temperature for the solid I-liquid, solid II-liquid and solid I-solid II transitions in the ammonium halides, in particular for NH 4 Cl. The critical behaviour of some other thermodynamic quantities is also predicted from the mean field theory.

Calculation of the T‐X Phase Diagrams for Binary Mixtures of Cholestanyl Myristate–Cholesteryl Myristate and Cholestanyl Myristate–Cholesteryl Oleate

“…As a general approach, by the mean field theory we are able to calculate the phase diagrams and to predict the observed behavior of the thermodynamic quantities close to phase transitions for any binary mixture of organic compounds. For the case of ammonium halides as molecular crystals, we recently derived the specific heat from the free energy and predicted their observed behavior near the melting point at high pressures 29 …”

“…Thus, the free energy of the (solid CO + liquid) phase is given by Eq. (29). Similarly, the free energy of the (solid CO + solid CnM) phase can be written as…”

First principle studies of ammonium chloride under high pressure

“…To investigate the nature of phase transition, scholars have made a great deal of effort experimentally [33][34][35][36][37][38][39][40][41][42][43] and theoretically. 44,45 The mechanism of order-disorder phase transition has been attributed to two possible orientations of ammonium tetrahedrons. 46 At room temperature and low pressure, NH 4 Cl adopts a CsCltype structure (phase II), in which NH 4 + ions are randomly distributed between two energetically equivalent orientations.…”

Calculation of a generalised smectic–hexatic phase diagram in liquid crystals

“…Using the mean field theory, we have calculated P-T [27,28] and T-X [29] phase diagrams in ammonium halides, ammonia [30], ice [31][32][33], and regarding the liquid crystals phase diagrams near the nematic-Sm A-Sm C (NAC) [34,35] and nematic-Sm A-Sm C* (NAC*) [36] point in our earlier studies.…”