Relativistic Density Functional Theory Investigations Of AgSi_n?n=1-21? Clusters And Bimetallic Endohedral Si₂₀ Cage

The geometries,stabilities and electron characteristics of AgSi_n?n=1-21?clusters and double transition metal atoms endohedral Si₂₀ fullerene-like cages have been systematically investigated.The research is based on density functional theory?DFT?,using the PW91 exchange association and the double-number polarization function group?DNP?set in generalized gradient approximation?GGA?theory.And the main results are as follows:The growth characteristics of AgSi_n?n=1-21?:The cluster is a two-dimensional planar structure when n ? 4.And it begins to grow in three-dimensional structure of blocks when n = 5.With the increase of the size of clusters,Ag atoms are gradually inserted into the Si cage and when n = 18,Ag atoms completely come into the Si cage forming Ag@Si_n structure;By analyzing the binding energy we find that for the same size of AgSi_n and pure-silicon clusters,the average atomic binding energy of AgSi_n is slightly higher than that of the pure silicon,which indicates that the addition of Ag atoms does not enhance the stability of the clusters;The consistency of the fragmentation energies of clusters and the second-order differences illustrates that:AgSi_n cluster shows maximum when n=5,10,13,15,18 which indicates that clusters in that stage are magic number clusters;Besides for the HOMO-LUMO energy gap value and chemical hardness analysis find that the energy gap value and chemical hardness of AgSi_n clusters is lower than that of pure Si clusters,which prove that atoms enhances the chemical activity of the clusters;The analysis of Hirshfeld charge shows that Si atom shares stronger electronegativity and takes electron,and Ag atom is electron donor.Heterogeneous 3d transition metal doped Si₂₀:?MM'?@Si₂₀?M = Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu and Zn?share the same structure of?MM'?@ Si₂₀ package structure.And by analyzing their binding energythe researcher find that the clusters' energy arelatively low with Ti and Co,and the energy of?TiCo?@Si₂₀ is the lowest.What's more,by comparing the bond length between the transition metals in?MM'?@Si₂₀ and that of the free-dimer,it is found that most of the bond length of thecage transition metal is longer than free-dimer's bond length.But there are also exceptions for instance,?ScZn?@Si₂₀,?TiZn?@Si₂₀,?CrZn?@Si₂₀,etc.Research on stability shows that Ti2@Si₂₀ clusters has the highest embedding energy and its average binding energy is relatively high,too.More importantly,it also has good symmetry,therefore,it is the most likely material which can be used as a base for nanomaterials.