Cuesta, J. A.Fernández Tejero, CarlosBaus, Marc2023-06-202023-06-201989-06-151050-294710.1103/PhysRevA.39.6498https://hdl.handle.net/20.500.14352/58898© 1989 The American Physical Society. One of us (M.B.) acknowledges the support of the Association EURATOM—Etat Belge and also of the Fonds National de la Recherche Scientifique. This work has, moreover, been partially sponsored by the Comisión Asesora de Investigación Científica y Técnica (Spain) Project No. PB85-0024.The orientational freezing of a system of hard ellipses, as a first approximation for a nematogen adsorbed on a smooth substrate, is studied with the aid of an approximate density-functional theory used previously for the study of hard ellipsoids. The isotropic-nematic transition, which was first order for the ellipsoids, is shown to proceed via a continuous transition in the case of the ellipses. We also show that when reducing the dimensionality of the angular space of ellipsoids, the width of the transition shrinks continuously and reaches zero only for a strictly two dimensional angular space.engjournal articlehttp://dx.doi.org/10.1103/PhysRevA.39.6498http://pra.aps.org/open access536OpticsPhysicsAtomicMolecular & chemicalTermodinámica2213 Termodinámica