Theoretical Study On The Structural Growth Sequence And Electronic Properties Of Arsenic And Antimony Clusters

In this paper,we have performed global search of the lowest-energy structures of Asn and Sbn clusters have been determined up to n = 24 and some medium-sized,such as 28,38,and 40,by using a combined technique of genetic algorithm global search and local minimization within density-functional theory(DFT)as implemented in the Dmo3 package,and employing VASP calculations for the geometry optimization and electronic properties.Starting from As9,we observed competition between structural patterns of fullerenelike cages,bulk fragment,core-shell structure and superclusters built by As8 units and an As2 bridge,while chain-like superclusters prevail in energy.These competing structural growth patterns have been further examined for the larger clusters at As28,As38,and As40.The chain-like superclusters become more energetically favorable than fullerene cages,bulk fragment and core-shell structure as cluster size increases.Remarkable even-odd oscillation behaviors were observed for the size dependence of cluster properties such as second differences of total energy,HOMO-LOMO gap,adiabatic electron affinities(AEA)and ionization potentials(AIP).The photoelectron spectroscopy of some small As clusters was investigated by using B3LYP/Gaussian.The computed photoelectron spectroscopies agree qualitatively with the measured data.For most sizes Sb clusters,the lowest-energy structures obtained for the structural growth patterns of cluster are the same as those previously found for Asn clusters by using same combined technique of genetic algorithm global search and local minimization within density functional theory.Due to the valence electron configuration,Sb atoms tend to form three bonds with the other Sb atoms in the equilibrium structure of Sbn clusters.Although Sbn and Asn clusters show substantial similarity in their structural properties,there is still a small difference between the Sb-Sb and As-As bonding,which leads to the different energy sequence for the structural isomers.The chain-like supercluster growth pattern is found to be dominant for the medium-size range with n=10-24,28,38,it would be interesting to further explore the transition from supercluster structure to bulk-like structure of As and Sb solid in the larger cluster size region.