The adsorption sites inside the metal-organic framework materials at increasing temperatures and pressures were explored. The results reveal that the adsorption sites are mostly determined by the interaction between the adsorbed molecules and the MOF frameworks at low temperature. As the temperature increases, it would be further influenced by the diffusion ability of the adsorbed molecules and the loading of molecules. The interaction energy of hydrogen molecules with the MOF-5 frameworks confirms that the Zn4O cluster plays the key role in the adsorption by pushing a probe molecule into the pore. (C) 2009 Elsevier B. V. All rights reserved.