2005 APS March Meeting
Monday–Friday, March 21–25, 2005;
Los Angeles, CA
Session B25: Focus Session: Computational Nanoscience II
11:15 AM–2:15 PM,
Monday, March 21, 2005
LACC
Room: 501A
Sponsoring
Units:
DMP DCOMP DAMOP
Chair: Talat S. Rahman, Kansas State University
Abstract ID: BAPS.2005.MAR.B25.1
Abstract: B25.00001 : Magic structures of binary metallic clusters
11:15 AM–11:51 AM
Preview Abstract
Abstract
Author:
Riccardo Ferrando
(Dipartimento di Fisica, Universita` di Genova)
The structure of binary metallic clusters is investigated by a variety of
computational tools, ranging from genetic and basin-hopping global
optimization algorithms, to molecular dynamics, and to density-functional
calculations. Three different binary systems are investigated: Ag-Cu, Ag-Ni,
and Ag-Pd. A new family of magic cluster structures is found. These clusters
have the common feature of presenting a perfect core-shell chemical
arrangement (with an outer Ag shell of monoatomic thickness) and of being
polyicosahedra, that is being made of interpenetrating icosahedra of 13
atoms. Core-shell polyicosahedra are of special stability, which originates
from the interplay of different factors. First of all, polyicosahedra are
very compact structures, so that they maximize the number of
nearest-neighbor bonds for a given size. However, in single-element
clusters, these bonds are not optimal, since inner bonds are strongly
compressed and surface bonds are expanded. This is the contrary of what is
required from the bond order -bond length correlation in metals, which
favors contracted surface bonds. In binary clusters, the situation is
different. Substituting the inner atoms of a single-element polyicosahedron
with different atoms of smaller size, the bonds can relax close to their
optimal distance. This leads naturally to the appearance of core-shell
polyicosahedra. In Ag-Cu, Ag-Ni and Ag-Pd the formation of these structures
is reinforced by the tendency of Ag atoms to surface segregation. A similar
mechanism of structural relaxation, originating from the interplay of
cluster geometry and bond order - bond length correlation, is also the cause
of the destabilization of icosahedral structures in pure Pt and Au clusters
. In these clusters, the compressed inner atoms of the icosahedra can relax
because of the formation of \textit{rosette }structures at vertices in the outer layer.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2005.MAR.B25.1