Within density functional theory with the general gradient approximation for the exchange and correlation, the bimetallic clusters AuPt and Au 6Pt have been studied for their structure and reactivity. The bond strength of AuPt lies between those of Au2 and Pt2, and it is closer to that of Au2. The Pt atom is the reactive center in both AuPt and AuPt+ according to electronic structure analysis. AuPt + is more stable than AuPt. Au6Pt prefers electronic states with low multiplicity. The most stable conformation of Au6Pt is a singlet and has quasi-planar hexagonal frame with Pt lying at the hexagonal center. The doping of Pt in Au cluster enhances the chemical regioselectivity of the Au cluster. The Pt atom essentially serves as electron donor and the Au atoms bonded to the Pt atom acts as electron acceptor in Au6Pt. The lowest triplet of edge-capped rhombus Au6Pt clusters is readily accessible with very small singlet - triplet energy gap (0.32 eV). O2 prefers to adsorb on Au and CO prefers to adsorb on Pt. O2 and CO have stronger adsorption on AuPt than they do on Au6Pt. CO has a much stronger adsorption on AuPt bimetallic cluster than O2 does. The adsorption of CO on Pt modifies the geometry of AuPt bimetallic clusters.
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