Structural distortion in thiol passivated gold clusters.
Several theoretical studies have been performed to investigate the effect of thiol passivation on gold nanoclusters. One approach consists of performing conjugate gradient structural DFT relaxations starting from different cluster-thiol monolayer configurations. Specifically, the Au28 and Au38 clusters coated with 16 and 24 methylthiol (SCH3) molecules, respectively, have been investigated. According to the DFT calculations performed on these passivated clusters, the effect of the thiol monolayer is strong enough to drastically distort the structure of the bare gold cluster.
In one calculation, a truncated octahedron Au38 cluster (with fcc symmetry) was dramatically distorted upon relaxation with 24 methylthiol molecules, symmetrically positioned on the (111) facets close to the hollow sites. The relaxed structure of the Au38(SCH3)24 cluster corresponds to a disordered, passivated nanocluster where the sulfur atoms of the thiol heads are incorporated within the cluster surface. The lowest-energy structure obtained from DFT structural relaxations of Au28(SCH3)16 also corresponds to a highly disordered passivated nanocluster with an ill-defined gol-thiol interface. It was obtained by the relaxation of the lowest-energy disordered structure of the bare Au28 cluster, with the methylthiols placed close to three-atom hollow sites.
"Chirality in Bare and Passivated Gold Nanoclusters"
I.L. Garzón, J.A. Reyes-Nava, J.I. Rodriguez-Hernandez, I. Sigal, M.R. Beltran, and K. Michaelian
Phys. Rev. B 66, 073403 (2002).
"Do Thiols Merely Passivate Gold Nanoclusters ?"
I.L. Garzón, C. Rovira ,K. Michaelian,M.R. Beltran, J.Junquera P. Ordejon, E. Artacho, D. Sanchez-Portal, and J.M. Soler
Phys. Rev. Lett. 85, 5290 (2000).
Distances of the gold (open diamonds) and sulfur (stars) atoms from the center of mass for the lowest-energy structure of the thiol-passivated Au28(SCH3)16 cluster the closed diamonds are included to show the degree of distortion and expansion of the gold metal cluster core upon passivation. the insets show the geometries of the chiral metal cores and the passovated clusters. Sulfur atoms are depicted as darker spheres
Two series of the lowest-energy isomer of Au at N=55. This cluster is a strongly rearranged and distorted 55-atom icosahedron.
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