Abstract
A global phase diagram of Maier-Saupe model for nematic-isotropic phase transition on an external field versus temperature plane is obtained, where due to non-polar property of the system two sets of order parameters and the conjugate fields are required to describe completely phenomena. The phase diagram is argued in the context of a similarity of the model to the three-state Potts model. Inhomogeneity of a thin system sandwiched by parallel walls is expressed in terms of effective external fields. Effects due to various anchoring walls, homeotropic, homogeneous, planer and oblique ones, are classified systematically on the basis of the phase diagram of bulk system. A shift of a transition temperature together with property of phase transition itself at the thin system is elucidated in relation to positions of a critical point and a tricritical one at the bulk.
