Adsorption thermodynamics of acrolein (CH2=CH-HC=O) on Pt (I 11) is investigated with adsorption free energy simulations as a function of temperature and pressure. This atomistic thermodynamic approach based on density-functional theory energies shows how adsorption modes and coverage are modified in realistic experimental conditions. The various adsorption modes of the multifunctional molecule show very similar free adsorption energies, suggesting the possible coexistence of various molecular structures on the surface. The qualitative trend shows a high coverage of eta(2) modes (adsorbed by the C=C bond only) at low temperature, evolving to a mixture Of eta(3)-cis and eta(4)-trans modes at lower coverage upon temperature increase. (c) 2005 Elsevier B.V. All rights reserved.