We conducted an improved Genetic Algorithm global search combined with the DFT study.A new and lower energy structures are reported;these new structures are found to exhibit core-shell structures with the number of core atoms increasing with cluster size.Matter of nanoclusters having different physical and chemical properties that can be different than their bulk counterparts;these properties are the consequence of particular geometrical structures,lower atomic coordination,large surface to volume ratios,and quantum confinement effects.Gold nanoclusters are probably the most extensively studied systems because the strong relativistic effects and significant s-d hybridization lead to a typical structures and properties.A great number of studies have been devoted to a deeper understanding of the structures on size-selected gold clusters and their size evolution,this knowledge is critical for the precise determination of their structure-catalytic relationship.

What is known about the geometry of metal nano clusters, such as gold, silver, palladium, platinum which are used for catalysis?

A couple of paragraphs on the   reported studies on the geometry of these clusters, experimental and theoretical studies.
             Over 100 molecules of nanoclusters like Au25(SR)18,Ag29(S2R)12,Au38(SR)24,Ag25(SR)18,Pt3,Pd3 known metal nano clusters.The study of the transition from 2D to 3D structures for gold clusters has a long history and has carried out by different methodologies. It is acknowledged that the 2D to 3D transition for AuN  happens at N= 12,11 and 8for the anionic ,neutral and                      cationic clusters respectively.The smallest clusters with the shell-like or hollow cage structures also depend on the charge.They have reported for anions (N = 16,17,18)  ,neutrals (N=17,18) and cations(N= 18,19).
  The structural determination of the Au20 cluster is a milestone which influence many other studies of medium sized gold clusters,it is highly symmetric tetrahedral pyramid with a large gap between  the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The next structural transition for anionic   and neutral gold clusters happens at N = 24,a size for which it has been proposed hollow-cage structure  and some of them can be considered as nanotubse.Recently theoretical studies state that Au27 and Au28 have tubular motifs for the neutral systems,while for  anions core-shell structures were found to fit better  the experiments data well as for Au30- and we know  that there are not theoretical studies of Au29 clusters.
   From the above discussion ,gold clusters exhibit very unusual geometries,making it necessary to perform  a good Global Minimum (GM) search of the potential energy surface to find the correct structures.The previous study which is carried out using semi empirical progress,unfortunately the semi empirical potentials are unable to reproduce the complexity of the electronic structure in bare gold clusters and can mislead the search of the most stable isomers even the lowest energy isomers were refined using ab initio methods.For that reason,GM search started to be carried out through codes directly coupled to DFT calculations,using methods like basin-hopping or GA.
      We analyze the lowest energy isomers of anionic and neutral clusters consisting of 27-30 gold atoms.The starting point of our implementation was the Birmingham Pool Genetic Algorithm(BPGA) developed by Johnston et al.In the case of fcc bulk lattice,crystalline clusters may take the form of octahedra or truncated octahedraNano crystalline structures are also possible,such as icosahedra,polytetrahedra and poly icosahedra.The lowest energy structure of the pure Au cluster is not icosahedral but a single copper impurity is sufficiently to stabilize the icosahedral structure of Au54Cu1,in case of Cu-Ag clusters of size 40,in which a specific core-shell poly icosahedral structure is stabilized.