Similarity and Dissimilarity between Influences of Anchoring Walls and   of External Fields on Nematic and Smectic A Phases
  The McMillan liquid crystalline models under the influence of homeotropic anchoring walls and of external fields are investigated. For thin systems, the existence of the critical thickness, below which the system does not undergo a discrete phase transition, is confirmed. Apparent differences between the influence of the anchoring walls and of external fields are elucidated by investigating the order parameters and a temperature vs external field phase diagram for the bulk systems. 
M. Torikai and M. Yamashita