The existing experimental data on the arrangement of Sn adatoms deposited on the Ru(0 0 0 1) substrate at room temperature are inconsistent: the earlier LEED, AES and LEISS measurements of Paffett et al. [J. Phys. Chem. 97 (1993) 690] recognized long-range ordered c(2 x 8) and (root 3 x 3)rect adsorbate patterns corresponding to local coverage theta=1/4 ML and theta=2/3 ML, respectively, whereas recent LEED and STM observations of Yuhara et al. [ Surf. Sci. 616 (2013) 131] indicated the formation of a c(2 x 8) structure with theta=3/8 ML, followed by a (root 3 x root 7) structure with theta=2/5 ML and an incommensurate Sn phase of somewhat similar geometry at larger overlayer densities. Motivated by this controversy, we employed first-principles DFT calculations to simulate the growth of Sn/Ru(0 0 0 1) films at submonolayer coverages. The optimal adatom configurations were found for increasing Sn coverage and contrasted with the structural models proposed in the literature. The computed surface phase diagram indicates that the characteristic 'zigzag-zigzag-zagzig-zagzig' arrangement of the c(2 x 8) phase corresponding to the local coverage theta=1/2 ML is energetically preferred at low Sn depositions, followed by the (root 3 x root 7) structure with theta=3/5 ML and the (root 3 x 3)rect structure with theta=2/3 ML, the latter constituting the most closely packed arrangement of the first wetting Sn layer. The DFT-predicted thermodynamically stable Sn/Ru(0 00 1) adsorbate configurations match well the available high-resolution STM images. The effect of Sn adsorption on the electronic characteristics of the Ru(0 0 0 1) surface is also explored, with special emphasis on adsorbate-induced modifications of the electron density-of-states distributions within the surface region. (C) 2014 Elsevier B.V. All rights reserved.