The Design Of New Materials Based On Cage-Like Cluster Assembling And The Investigation Of Their Physical Properties

With the development of experimental technology, it is possible to construct a newmaterial with desirable properties by using the approach “from bottom up” with nano-clusters serving as the building blocks. Compared with the traditional materialsconstructed by element atoms, cluster-assembled materials built from special clustershave doublly controllable dimension to tune their properties and function, i.e., thestructure and properties of the building blocks are controllable, and the cluster-clusterinteraction are controllable. Due to the novel quantum effect of nano-clusters (physicaland chemical properties change with the geometry, size, charge and component), clusterassembly is considered as one of the most promising ways to design or exploit newfunctional materials. In this paper, using first principles calculations based on densityfunctional theory and research mentality of “selection of building blocks�'design ofassembly�'analysis of physical properties�'simulation of application”, we carry outa systematic investigation on the structures, stabilities, electronic and magneticproperties of some cluster-assembled materials constructed from three kinds of cage-like clusters (i.e., In12As12, ZnkOkand V@Si12) so as to deal with some problems in thedesign theory of cluster assembly. The main contents and results are as follows:(1) By using the unbiased Saunders “kick” method, the lowest energy structure ofInnAsn(n=1-15) clusters are determined at DFT/B3LYP/LANL2DZ theoretical level.Analysis of their relative stability shows that the sodalite cage cluster In12As12, withhigh symmetry (Th), has very high stability, and is a magic cluster. Taking this specialcluster as building blocks, we have designed and characterized a new family of stablenanomaterials with different dimensions, such as the dumbbell chain nanowire-I, thezigzag chain nanowire-II, the graphene-like porous cluster monolayer with molecularseiving function, and the FAU-InAs crystal with structural characteristics of zeolite. Inthese cluster-assembled materials the adopted cluster-cluster interaction is the moststable “6MR to6MR”, i.e., H-H1, link. The sodalite cage structure of building block andits wide energy gap can be well retained in all of these In12As12-assembled materials.Therefore, they are all wide band gap semiconductor materials. Compared with theground state of ZB-InAs, the relative band gap value is about2.00-4.89(Eg/Eg, ZB).(2) On the basis of the characterized magic cage-like clusters ZnkOk(k=12,16) fromglobal optimum algorithm, we have designed and characterized all possible ZnkOk- assembled materials with different stable cluster-cluster interaction (i.e., H1, H2, C and S,or H’, C’ and S’) by using a new method of “unbiased topology search”. On thestructure, the eleven kinds of ZnkOk-assembled polymorphs are all low-densitynanoporous materials. Their pore volume range from0.007cm3g-1to0.289cm3g-1, andspecific surface area range from164m2g-1to1870m2g-1. Interestingly, some of thesepolymorphs, such as SOD, LTA and Tet-Zn16O16, are even more stable than thesynthesized ZnO phase. Moreover, they have good dynamic stability, mechanicalstability and thermal stability. The electronic calculations indicate that all of the ZnkOk-assembled polymorphs are wide band gap semiconductors with a direct or indirect bandgap values of2.58eV-3.23eV (modified by HSE06).(3) Taking the experimentally characterized transition metal atom endoheral siliconcage-like clusters V@Si12as alternative building blocks, we have confirmed thefeasibility of V@Si12serving as building bocks of2D room temperature ferromagneticmaterials through the investigation of its structure, stability, electronic properties andmagnetism. On the basis of this, we have designed and characterized two kinds ofstable V@Si12-assembled sheets by using the method of “unbiased topology search”.These two sheets can be described as: hexagonal porous sheet PS (the diameter of poreis9.33) and honeycomb sheet HS. The endoheral cage-like structure of buildingblocks can be well maintained in both of these two sheets. Since the bound of energybarrier of Si12cage, the center V atoms in the2D structures well realize a regular andseparate distribution. The calculations of magnetism show that the magnetic moment ofbuilding blocks in PS and HS is3.5μBand3.8μB, respectively. The magnetic couplingbetween these local magnetic moment is long-range ferromagnetic. In addition, thespin-polarized first principles molecular dynamics simulations show that theferromagnetic coupling of PS sheet is stable at room temperature. By using the mean-field theory, the estimated value of the Curie temperature is803K.Since most of the designed new materials have nanoporous characteristics, they willbe promising for the applications of molecular transport, gas storage, atomic control andheterogeneous. Hollow structure characteristics of the building blocks In12As12andZnkOkwill also make their assembled materials having advantage for endohedral doping.Moreover, by using the way of cluster assembly, we have realized, for the first time, the2D silicon-based room-temperature ferromagnetic ordering structure, which highlights anew avenue to exploit new2D spintronics nanomaterials.