Landau theory of phase transitions

Landau theory of phase transitions describes how materials change states (like from a liquid to a solid) by analyzing an order parameter—an indicator of the system's symmetry. It uses a mathematical function called the free energy, expanded as a series in the order parameter, which changes as the temperature varies. When the free energy favors a non-zero order parameter, a phase transition occurs. The theory explains whether the transition is smooth or abrupt, and helps understand critical behavior near transition points, providing a framework to predict and categorize different types of phase changes.