  Density-functional-theory calculations for the adsorption of molecular
nitrogen on ruthenium surface are reported. It is found that nitrogen molecule
is adsorbed while standing perpendicular to the triangular surface of
ruthenium. The doping by K atoms favours the adsorption of molecular nitrogen.
The calculation of the adsorption energy has also been performed on iron and
osmium clusters which shows that ruthenium adsorbs better than iron or osmium.
It is found that potential for atomic nitrogen is deeper and more stable than
that of molecular nitrogen and hence atomic nitrogen is important for
catalysis.
