  A Monte-carlo (MC) simulation procedure has been developed where the pair
bond energies are allowed to take into account the various coordination numbers
of surface atoms and the presence of adsorbates. The pair bond energies are
calculated from partial bond energies of atoms which, in turn, are calculated
from modified tight binding model in the second moment approximation. The model
has been applied to study the role of adsorption of hydrogen, oxygen, carbon
monoxide and nitric oxide on the surface composition and surface bond geometry
of bimetallic Pd-X (X = Ag, Cu, Ni, Pt) nanoparticles having fcc
cubo-octahedral geometry with 201, 586, 1289 and 2406 atoms. The results are
compared with the known experimental results. Importance of the results in
studying reactions on supported bimetallic catalysts has been highlighted.
