Density Functional Theory Study Of W_nCo_0,±（n=1～6） Clusters

In this paper, Gaussian03program based on density functional theory is applied. Thegeometric structures of W_nCO（n=1～6） clusters and W_nCO^±（n=1⁶） clusters are alloptimized systematically, the ground state structures and the physical and chemicalproperties are investigated. The main results are as follows:（1） The ground state structures of W_nCO clusters are generated when CO is adsorbedon W_nclusters or anionic clusters. We found that among the molecular adsorption statesexists mainly in the form of end-on type geometry; the bridge site adsorption type geometryplays a supplementary role. On the face of the adsorption is a non-dissociative adsorption.The CO bond length increased0.120～0.123nm in W_nCO clusters （compared with0.116nm in free CO molecule）, which demonstrated the CO are activated. The stability analysisshows that W3CO and W5CO clusters are more stable than other clusters; Natural bondorbital （NBO） analysis indicate that the interaction between W atom and CO molecule isprimarily contributed by hybridization of molecular orbits within CO and6s、5d、6p and6dorbital of W atoms.（2） Based on the ground state structures of W_nCO clusters, the vibrationalspectrum、polarizability、the magnetic moment、the rmodynamic properties and orbitallevel are analyzed. The results show that the IR spectrums modes of the strongest intensityof clusters which we studied are similar to each other, are assigned to CO stretching mode,and the wavenumber range is between1670cm-1and1850cm-1；The Raman spectrumgraphics of the W_nCO （n=1～6） clusters are different to each other. The polarizabilityvalues in xx、 yy、 zzdirection are major components in each cluster. The total magneticmoment of W_nCO （n=1～6） clusters varies from0-4μB, the magnetic moment of W_nCO（n=1～6, n≠1,5） clusters is quenched. The NICS values of W1CO、W2CO and W5CO arepositive numbers, so they have anti-aromaticity; While NICS values of W3CO and W4COclusters are negative numbers, which have aromaticity. The enthalpy of formation for allthe clusters are negative, so they are stable on thermodynamics; The total wiberg bondindex （WBI） and W average wiberg bond index （WBI） increase monotonically with theincrease of cluster size. The molecular orbit between Alpha and Beta in clusters W4CO andW6CO is complete degenerate, and a closed-shell configuration for the W2CO and W3COclusters. （3） The structures character、stability and chemical activity of W_nCO^±（n=1⁶） clustershave been studied. The result indicates that when n≥2, the ground-state structures ofW_nCO^±（n=1⁶） clusters transform from double-dimensional （2D） to three-dimensional （3D）;when2≤n≤4, the ground-state structures of anionic and cationic clusters are different whenthey have the same atomic sizes. The CO bond length in anionic calusters is larger thancationic clusters. With the increase of cluster size （increased size）, the stabilities of cationicclusters increased; however, the chemical activities of cationic clusters have no regularities.There are “magic number” effects in anionic calusters, and the magic number is3and5.According to the charge character and wiberg bond index （WBI） analysis, the W atom is akey to decide the electrical property of W_nCO^±（n=1⁶） clusters; the total wiberg bond index（WBI） increase monotonically with the increase of cluster size. The IR spectrums modes ofW_nCO^±（n=1⁶） clusters which we studied are similar to each other, But the Ramanspectrum graphics of the W_nCO^±（n=1⁶） clusters are different to each other.To sum up, in this paper we have systematically studied the physical and chemicalproperties of the ground state of clusters, and revealed the internal relation betweenmicrostructure and macro-properties on W_nCO（n=1～6） clusters and W_nCO^±（n=1⁶） clusters.This article could provide a reliable theoretical basis for experimental research and anappropriate model for developing new catalytic functional materials.