Charge transfer and adsorption energies in the iodine–Pt(1 1 1) interaction Alexandre Tkatchenko, Nikola Batina, Andre ´s Cedillo, Marcelo Galva ´n * Departamento de Quı ´mica, Divisio ´ n de Ciencias Ba ´ sicas e Ingenierı ´a, Universidad Auto ´ noma Metropolitana—Iztapalapa, Av. San Rafael Atlixco 186 Col. Vicentina, AP 55-534, Me ´xico DF 09340, Mexico Received 26 July 2004; accepted for publication 18 February 2005 Available online 10 March 2005 Abstract The adsorption energies for iodine atom on the fcc, hcp, bridge, and atop sites of the Pt(1 1 1) surface were deter- mined using ab initio DFT method in two different unit cells. A periodic slab model is used and the obtained energies are in agreement with the corresponding experimental values extrapolated at 0 K. The charge transfer is determined by the use of the Hirshfeld partitioning scheme, and the charge transfer values follow the adsorption energy trend for dif- ferent sites of the Pt(1 1 1) surface. The results show that the plane-wave DFT approach correctly describes the adsorp- tion of iodine on the Pt(1 1 1) surface and support the use of the Hirshfeld method in surface science problems. Ó 2005 Published by Elsevier B.V. Keywords: Pt(111); Hirshfeld partition; Charge transfer 1. Introduction The adsorption of iodine on Pt(1 1 1) surface has been studied extensively by many experimental techniques [1–8] but only a very few theoretical ab initio studies exist on the subject [9,10]. The interest in this system can be explained by the fact that the experimental procedures for its prepara- tion and characterization are well established, yet it presents a structural richness, having four distinct structural phases at different coverage: ( p 3 · p 3)R30, ( p 7 · p 7)R19.1, (3 · 3)-sym. and (3 · 3)-asym., each of them is characterized by one or several specific adsorption sites [1,5,6]. Also, same results are obtained in vacuum, air and solution environments [7]. Although the experimental results on this system are very con- vergent, many answers remain to be obtained from theory related to its chemistry and structural arrangement. For instance, the nature of I–Pt bond for different adsorption sites, Pt surface 0039-6028/$ - see front matter Ó 2005 Published by Elsevier B.V. doi:10.1016/j.susc.2005.02.032 * Corresponding author. Tel.: +52 55 58046413; fax: +52 55 58046415. E-mail address: mgalvan@xanum.uam.mx (M. Galva ´n). Surface Science 581 (2005) 58–65 www.elsevier.com/locate/susc