In this paper, we report the results of surface relaxation investigations for a clean Pt(1 1 1) as well as Pt(1 1 1) covered with a pseudomorphic monolayer of Cu. The pseudomorphic (1 x 1) Cu overlayer on Pt(1 1 1) was formed upon continuous copper adsorption at the substrate temperature equal to 450 K. Considerations include both the experimental and theoretical studies employing directional elastic peak electron spectroscopy (DEPES), multiple scattering (MS) formalism, and density functional theory (DFT). A quantitative analysis of two-dimensional DEPES intensity distributions is presented and the contribution of consecutive subsurface Pt atomic layers to the measured signal is identified. The experimental DEPES distributions are compared with theoretical maps MS-simulated for a variable separation between the outermost atomic planes. For the clean Pt(1 1 1), the best fit is obtained assuming the outward relaxation of the surface layer by +0.7% with respect to the interplanar distance in the bulk, confirming the slight expansion of the Pt(1 1 1) surface. Similar analysis performed for the Cu/Pt(1 1 1) adsorption system indicates the inward shift of the pseudomorphic Cu overlayer by -6.9% with respect to the substrate lattice continuation sites. Such DEPES-determined surface relaxations of Pt(1 1 1) and Cu/Pt(1 1 1) agree with the values predicted by the corresponding DFT computations. (C) 2015 Elsevier B.V. All rights reserved.