We have performed embedded atom calculations for a number of systems of ele
ctrochemical interest involving a metallic single-crystal substrate and a m
etallic adsorbate. Different thermodynamic contributions to the so-called u
nderpotential shift are calculated and analyzed comparatively, drawing some
general trends. The metal pairs considered involve silver, gold, platinum,
palladium and copper. We consider the possibility of underpotential deposi
tion through the excess of binding energy, arriving at two novel conclusion
s. First, for some systems consisting of metal M-1 and M-2, underpotential
deposition should be energetically possible in both cases, that is M-1 on M
-2 and M-2 on M-1. Second, anions may play a decisive role in changing the
energetics of some systems. In particular cases like copper on Au(lll) they
may be responsible to a large extent for the existence of an underpotentia
l deposition. Entropic contributions were neglected in the present analysis
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