In this article, we obtain the adiabatic potential energy of a hydrogen atom on a Pd3Ag(111) surface and in its subsurface by first principles calculations based on the density functional theory. Moreover, we discuss the difference between the behaviors of the hydrogen atom on Pd(111) and on Pd3Ag(111) surfaces by comparing the calculation results. The results show that the potential energy value increases when the hydrogen atom is located at a site where some of the surrounding atoms are Ag atoms. In addition, the potential energy minimum and the energy barrier into the bulk area of Pd3Ag(111) surface are lower than those of the Pd(111) surface. The decrease of these values is caused by the lattice expansion due to Ag alloying. (C) 2007 Elsevier B.V. All rights reserved.