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Studies on Electronic Structure of Clusters by Density Functional Theory

Author: YuanZuo
Tutor: ChengLongJiu
School: Anhui University
Course: Analytical Chemistry
Keywords: density functional theory electronic structure sandwich compound Aunanocluster aromaticity
CLC: O641
Type: Master's thesis
Year: 2014
Downloads: 5
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Abstract


Clusters have the sizes between ones of atoms and macroscopical systems, and own the outstanding physical and chemical properties, so studies on clusters have gradually evoked great interest in recent years. With the quick development of computational methods and computer technology, so studying geometry, electronic structures and many other properties of clusters are dependent on computational chemistry. And because density functional theory owns moderate computational consume and high precision, it has become one of the most important computational methods in theoretical chemistry.In this paper, we analyze the electronic structure of three clusters with special structure and property (B142+、Cr(B12)2and phosphine-protected Au20nanocluster) detailedly.The main studies are as follows:1. Study on electronic structure of B142+——A magic number double-ring clusterBased on the previous study on neutral B14cluster, surprisingly, we find that B142+is a "magic number" cluster with double-ring structure, which has the largest HOMO-LUMO gap(3.31eV) and the highest aromaticity in double-ring clusters. This double-ring B142+cluster is energetically lower than the quasi-planar one by even-1.2eV using density functional theory. The40delocalized valence electrons of Bu2+fill electronic shells as in Al13-cluster based on the jellium model. The reasons for the unusual properties of the double-ring B142+may be radial and tangential Huckel’s aromaticity and the effect of jellium model.2. Ferrocene analogues of sandwich B12·Cr·B12:A theoretical studyThe bowl B12cluster was previously reported to be analogous to benzene and predicted to be one of the best candidates to be new inorganic ligands. The structural stability and electronic properties of a new sandwich compound Cr(B12)2(D3d) have been investigated by using density functional theory. It is found that the sandwich Cr(B12)2(D3d) is a stable complex with large binding energy (-5.93eV) and HOMO-LUMO gap (2.37eV), as well as Fe(C5H5)2and Cr(C6H6)2, following the18-electron principle. The detailed molecular orbitals and aromaticity analyses indicate that the sandwich compound Cr(B12)2(D1d) is electronically very stable. The natural bond orbital analysis suggests that spd-π interaction plays an important role in the sandwich compounds.3. Electronic Stability of Phosphine-Protected Au20Nanocluster:Superatomic BondingA recent experiment reported that a newly crystallized phosphine-protected Au20nanocluster [Au20(PPhy2)10Cl4]Cl2[PPhpy2=bis(2-pyridyl)phenylphosphine] owns a very stable Au20core, but the number of valence electrons of the Au20core is14e, which is not predicted by the superatom model. So we apply the density functional theory to further study this cluster from its molecular orbital and chemical bonding. The results suggest that the Au20(+6) core is an analogue of the F2molecule based on the super valence bond model, and the20-center-14-electron Au20(+6) core can be taken as a superatomic molecule bonded by two11-center-7-electron superatoms, where the two11c superatoms share two Au atoms and two electrons to meet an8-electron closed shell for each. The electronic shell closure enhances the stability of the Au20core, besides the PN bridges. Exceptionally, the theoretical HOMO-LUMO gap (1.03eV) disagrees with the experimental value (2.24eV), and some possible reasons for this big difference are analyzed in this paper.

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