  The effect of hydrogen adsorption on the magnetic properties of an Fe$_3$
cluster immersed in a Cu(111) surface has been calculated using densifty
functional theory and the results used to parametrize an Alexander-Anderson
model which takes into account the interaction of d-electrons with itinerant
electrons. A number of adatom configurations containing one to seven H-atoms
were analyzed. The sequential addition of hydrogen atoms is found to
monotonically reduce the total magnetic moment of the cluster with the effect
being strongest when the H-atoms sit at low coordinated sites. Decomposition of
the charge density indicates a transfer of 0.4 electrons to each of the H-atoms
from both the Fe-atoms and from the copper substrate, irrespective of
adsorption site and coverage. The magnetic moment of only the nearest neighbor
Fe-atoms is reduced and mainly due to increased population of minority spin
d-states. This can be modeled by increased indirect coupling of d-states via
the conduction s-band in the Alexander-Anderson model.
