Binary clusters AuPt and Au₆Pt: Structure and reactivity within density functional theory

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.