Theoretical surface physics - Bjørk Hammer¶
Recent research projects by Bjørk Hammer:
We are conducting research within theoretical surface science.
One of the major challenges is to understand how surfaces of metal,
alloys and compounds react with gas molecules.
Here an H2 molecule is reacting at a gold surface. The reaction is
hindered by a large energy barrier reflecting the nobleness of the
surface.
Here the chemical bonding of CO at a Pt surface
is investigated. Even though we normally think
of Pt as a noble metal, it is actually capable
of forming strong bonds to some molecules and
atoms.
The molecular orbitals are changed dramatically
upon adsorption of the CO molecule at a metal
surface. In particular the 2pi* orbital of the
CO which is empty in the gas phase is found to
change upon adsorption. It aquires a considerable
filling and is responsible for much of the
bonding of the molecule to the surface.
Phys. Rev. Lett. 76, 2141 (1996).
Our newest studies show that the reactivity of
atomic step edges is much higher than the
reactivity of planar surfaces. In terms of
the reaction rate at room temperature, a
Ru step edge atom is up to 10 orders of magnitude
more reactive for breaking of an NO molecular
bond compared to a Ru(0001) atom.
Phys. Rev. Lett. 83, 3681 (1999).
The description of the surface properties of
metals, alloys, and compounds and of the
reaction properties of molecules requires a
most accurate calculational method. We use
the density functional theory method founded
by Nobel laureate, W. Kohn. The electron-
electron exchange-correlation interaction
is approximated in the theory and is under
constant development.
We have recently proposed a new exchange-
correlation description (RPBE) which is
proving to be very accurate both for the
surface properties and for the molecular
bond energies. In particular, the overbinding
of small molecules is reduced as is the
overbinding of adsorbates at surfaces.