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Surface Science 410 (1998) 151157 The reconstruction of Rh(001) upon oxygen adsorption

Summary: Surface Science 410 (1998) 151­157
The reconstruction of Rh(001) upon oxygen adsorption
D. Alfe` a,*1, S. de Gironcoli a, S. Baroni a,b
a INFM ­ Istituto Nazionale di Fisica della Materia and SISSA ­ Scuola Internazionale di Studi Superiori ed Avanzati, via Beirut 2­4,
I-34014 Trieste, Italy
b CECAM, ENSL, Aile LR5, 46 Alle´e d'Italie, F-69364 Lyon, Cedex 07, France
Received 24 October 1997; accepted for publication 19 January 1998
We report on a first-principles study of the structure of O/Rh(001) at half a monolayer of oxygen coverage, performed using
density functional theory. We find that oxygen atoms sit at the center of the black squares in a chess-board c(2×2) pattern. This
structure is unstable against a rhomboid distortion of the black squares, which shortens the distance between an O atom and two
of the four neighboring Rh atoms, while lengthening the distance with respect to the other two. We actually find that the surface
energy is further lowered by allowing the O atom to get off the short diagonal of the rhombus thus formed. We predict that the
latter distortion is associated with an order­disorder transition, occurring below room temperature. The above rhomboid distortion
of the square lattice may be seen as a rotation of the empty white squares. Our findings are at variance with recent claims based on
STM images, according to which it is instead the black squares which would rotate. We argue that these images are indeed
compatible with our predicted reconstruction pattern. © 1998 Elsevier Science B.V. All rights reserved.
Keywords: Chemisorption; Density functional calculations; Oxygen; Rhodium
1. Introduction tion. Oxygen adsorption on Rh(001) is known to
be dissociative and to saturate at half a monolayer,


Source: Alfè, Dario - Departments of Earth Sciences & Physics and Astronomy, University College London


Collections: Physics; Geosciences