Density Functional Theoretical Studies On The Electronic Structure And Properties Of The Ligand-Free Transition-Metal Clusters

Transition-metal clusters are a kind of ideal model for studying the surface science andmany solid properties on the level of molecule. Especially,bare transition-metal clustershas not only magnificent magnet but also high reactivity,which has resulted in greatattention about its structures and properties. The essence of structure for ligand-freetransition-metal clusters has been partially revealed by DFT (density functional theory)in which the relation between its electronic structure and properties has been elucidated.i. The current studies on ligand-free transition-metal clusters has been reviewed inthis paper.ii. At the first time we has systematically studied electronic structure and many properties of ligand-free transition-metal clusters from La through Au,by using the cluster model on the level of B3LY1VLANL2DZ. These properties include bind energy,electronic affinity,ionization potential,atomic distance and magnetic property. The conclusions are drawn below.(1) The variation trend of binding energies,bond length,electronic affinity and ionization potential for sixth series of whole transition-metal clusters (except of Hg) are good agreement with that of experimental value for the corresponding metals.(2) The variation trend of magnetic moment for clusters nonmonotonously increases or decreases while atomic numbers augment. During these clusters,there some clusters have nonzcromagnet. However,the moment of Os and Ir clusters is bigger than that of other clusters in sixth series of transition-metal clusters.(3) The value of clusters' gap between highest occupied molecular orbits (HOMO's) and the lowest unoccupied molecular orbits (LUMO's) is not obviously relative to atomic number of clusters.iii. Full optimization geometry structures of Fen (n=2-6) have been performed on the level of B3LYP/STO-3G. The properties of iron clusters have been accurately studied. Some results are shown as follows.(1) The ground states show equilibrium bond distances substantially shorter than the distance in the crystal,2.48 A. Bond distances of clusters of the ground state monotony increase as cluster size augments.(2) For the ground states magnetic moments of clusters enhanced over the bulk value,by 22-45%. Magnetic moments increase while the size of clusters increases,but the amplitude little by litter reduces. The energy of clusters of the nonmagnetic sate,which keep the similar structure of the ground state,are higher that of the ground states,but the bond distances of clusters of the nonmagnetic sate are shorter than that of the ground ones. The maximization of the number of nearest-neighbor bonds (ISNB) and the gain in magnetic energy drives the iron cluster toward compact high-dimensional geometries. It has been also found that compact structures of clusters are more stable than the geometrical structures of the iron bcc (body-center cubic) lattice.(3) It is evident that the variation trend of electronic affinity for iron clusters monotonously augments as the clusters size increase. However,on the contrary,the variation trend of the ionization potential of clusters obviously monotonously diminishes with the decreasing of cluster sizes. The binding energy of Fe6 cluster nonmonotonously enhances while magnetic moment increases.(4) The IR vibratory frequencies of clusters lessen as the cluster size increases,but the number of peak increases during the augment of the cluster size.