Surface stress changes in the Ir(001)/H system: Density functional theory study

Abstract

Density functional theory calculations of the surface energy and surface stress changes associated with the formation of the Ir(001)(5 \ifmmode\times\else\texttimes\fi{} 1)-hex clean-surface reconstruction and its transformation to a (5 \ifmmode\times\else\texttimes\fi{} 1)-added row (AR) structure in the presence of adsorbed atomic hydrogen have been performed and compared with experimental results. The calculations clearly show that the clean-surface (1 \ifmmode\times\else\texttimes\fi{} 1)-to-(5 \ifmmode\times\else\texttimes\fi{} 1)-hex reconstruction is not driven by a reduction in tensile surface stress. While the surface energy is reduced by this transformation, the surface stress increases; proper convergence of the calculated surface stress requires the use of slabs containing at least nine atomic layers, due to the substantial subsurface relaxations associated with the (5 \ifmmode\times\else\texttimes\fi{} 1)-hex phase. By contrast, the H-induced reconstruction leads to a calculated reduction in the tensile surface stress in the range 1.76--2.06 Nm${}^{\ensuremath{-}1}$ for an H coverage range of 0.6--0.8 ML, in excellent agreement with the experimentally determined value of 1.7 Nm${}^{\ensuremath{-}1}$.