Adsorption behavior on the GaAs(0 0 1)-c(4 x 4) surfaces is systematically investigated by using our ab initio-based approach and the Monte Carlo methods. The change in stable structure of the c(4 x 4) surfaces is clarified by considering adsorption or desorption of surface dimers as functions of temperature and As pressure. The calculated results imply that the c(4 x 4) surface with As dimers is stable at low temperatures less than similar to400 K, whereas the surface with Ga-As dimers is stabilized at high temperatures in the range of similar to400-700 K. The disordered dimer arrangements consisting of Ga and As substituted by each other in the c(4 x 4) unit cell hardly appear even at high temperatures such as similar to800 K. We also investigate the behavior of Ga and As adatoms on these c(4 x 4) surfaces. The calculated results reveal that Ga atoms can adsorb and migrate on the surfaces while desorption of As adatoms proceeds without sufficient migration. Therefore, Ga adatoms play an important role for the epitaxial growth of GaAs on the GaAs(0 0 1)-c(4 x 4) surface. (C) 2004 Elsevier B.V. All rights reserved.