Systematic Density Functional Study of the Adsorption of Transition Metal Atoms on the MgO(001) Surface
Received: August 14, 1996 Revised October 9, 1996 Abstract: We report the results of nonrelativistic and relativistic
gradient-corrected density functional calculations on
the interaction of single transition metal atoms with the oxygen sites
of the regular MgO(001) surface. The
surface has been represented by stoichiometric clusters of ions
embedded in large arrays of point charges.
Two adsorption sites have been considered, the on-top adsorption
on the oxide anion and the bridge adsorption
over two adjacent oxide anions; on-top adsorption is found to be
energetically preferred. The metal atoms
considered are Cr, Mo, W; Ni, Pd, Pt; Cu, Ag, and Au. These
adsorbates can be classified into two groups
depending on the strength of the bond with the surface. Cu, Ag,
Au, Cr, and Mo exhibit weak or very weak
bonds of the order of one-third of an electronvolt; their interaction
is due to polarization and dispersion with
little mixing with the substrate orbitals. Ni, Pd, Pt, and W, on
the other hand, form relatively strong bonds,
of the order of 1 eV, with the oxide anions. This bond has a
covalent polar nature with little charge transfer
from the metal to the oxide. This is consistent with the fact that
MgO is a wide gap insulator with very weak
oxidizing power. The consequences of the different bonding
mechanisms for the growth of metal particles
on this oxide surface are discussed.
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