A new analytical potential energy surface for the adsorption system
CO/Cu„100…
Roberto Marquardt,
1,a͒
Frédéric Cuvelier,
2
Roar A. Olsen,
3
Evert Jan Baerends,
4
Jean Christophe Tremblay,
5
and Peter Saalfrank
5
1
Laboratoire de Chimie Quantique, Institut de Chimie, UMR 7177 CNRS/UdS, Université de Strasbourg 4,
rue Blaise Pascal, 67000 Strasbourg, France
2
Laboratoire de Modélisation et Simulation Multi Echelle, Université Paris-Est Marne-la-Vallée,
b͒
5 Bd Descartes (Champs-sur-Marne), F-77454 Marne-la-Vallée Cedex 2, France
3
Gorlaeus Laboratory, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden,
The Netherlands and Akerhus University College, P.O. Box 423, 2001 Lillestrøm, Norway
4
Theoretische Chemie, fac. FEW, Scheikundig Laboratorium, Vrije Universiteit, De Boelelaan 1083,
1081 HV Amsterdam, The Netherlands
5
Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, 14476 Potsdam-Golm, Germany
͑Received 15 October 2009; accepted 13 January 2010; published online 18 February 2010͒
Electronic structure data and analytical representations of the potential energy surface for the
adsorption of carbon monoxide on a crystalline copper Cu͑100͒ substrate are reviewed. It is found
that a previously published and widely used analytical hypersurface for this process ͓J. C. Tully, M.
Gomez, and M. Head-Gordon, J. Vac. Sci. Technol. A 11, 1914 ͑1993͔͒ represents rather poorly the
data obtained from a slab type calculation of the electronic structure. A new, global analytical
representation of the potential energy surface for this process is derived via a nonlinear adjustment
of parameters. It is more general and fits qualitatively better the electronic structure data. Key
characteristic elements of the new surface are the “top” equilibrium adsorption site in the
perpendicular arrangement Cu–C–O with Cu–C and C–O distances of 184 and 115 pm, the
desorption energy of 0.76 eV and the barrier for lateral diffusion of 33 meV, including
approximative corrections for the variation of zero point energy. Anharmonic vibrational
fundamentals and overtones are also calculated from six dimensional variational calculations. All
these values agree equally well or better with experimental data than previous published theoretical
data within estimated uncertainties. The analytical representation is compact and robust, and may be
used to describe other adsorption processes of diatomic molecules, including dissociative
chemisorption. © 2010 American Institute of Physics. ͓doi:10.1063/1.3308481͔
I. INTRODUCTION
Reactive and nonreactive molecular adsorption on metal
or metal-oxide substrates are essential elementary steps in
heterogeneous catalysis, which received increasing scientific
attention, both because improved experimental
1–4
and theo-
retical techniques
5–7
made more detailed investigations pos-
sible in the past two decades, and because of their important
implication in the chemical industry. Effort has been focused
on the energetic aspects of the underlying kinetics, in par-
ticular the determination of adsorption or reaction activation
energies, while dynamical aspects have often been less well
studied.
8
A widely studied class of systems involve the reactive or
nonreactive scattering of diatomic molecules from metal sub-
strates, the dynamics of which is studied theoretically within
the Born–Oppenheimer approximation. While the validity of
this approximation remains an open question in many cases,
the need for accurate potential energy surfaces ͑PES͒ to
simulate the nuclear motion of the adsorbed species during
and after adsorption in the electronic ground state is an un-
contested, valuable first approach to model and to understand
the complex kinetics of these processes.
Quite generally PES may be derived from calculations of
the electronic structure, from a direct modeling of experi-
mental data, or from a mixture of both. To our knowledge,
PES for adsorption processes of diatomic molecules, or low
dimensional sections thereof, have been determined mainly
from ab initio calculations of the electronic structure. Accu-
racy is limited by the quality of the ab initio calculations and
the type of models used. Slab type calculations allow to de-
scribe periodic patterns of adsorbed species normally in non-
zero coverage models. Cluster type calculations aim to de-
scribe the adsorption interaction per adsorption site in the
zero coverage limit. Currently preference is given to slab
type calculations because of convergence issues,
9
including
quasi-three-dimensional ͑3D͒-supercell calculations.
For the purpose of studying the kinetics of adsorption
and of the adsorbed species on the substrate, global analyti-
cal representations of the PES are useful. Main advantages of
analytical representations are their versatility in dynamics
calculations and their adaptability to experimental data via
an appropriate adjustment of parameters. For adsorbed di-
a͒
Author to whom correspondence should be addressed. Electronic mail:
roberto.marquardt@unistra.fr.
b͒
Previously Laboratoire de Chimie Theorique, Université de Marne-la-
Vallée.
THE JOURNAL OF CHEMICAL PHYSICS 132, 074108 ͑2010͒
0021-9606/2010/132͑7͒/074108/17/$30.00 © 2010 American Institute of Physics132, 074108-1