A Density Functional Theory Study For W_nCO^0,±（n=7-12） Clusters

This article is based on density functional theory(DFT), using Gaussian03 quantum chemistry program, choosed the hybrid density functional B3 LYP method, LANL2 DZ pseudo-potential basis set to optimize WnCO±(n=7-12) clusters adsorption system configuration. On the basis of ground state structure, the author going to study the system’s stability, adsorption activity and physical chemistry properties. The main results are as follows:(1) The ground state structure of WnCO(n=7-12) clusters adsorption system is combination with Wn(n=7-12) clusters ground state structure and a CO molecule. after the CO adsorption, W clusters matrix don’t have a big changes. the greater clusters size, the stronger of ability to maintain the original structure of W clusters. but in terms of symmetry, the point group of WnCO system is lower compared with Wn clusters. The type of CO molecules adsorbed on W clusters is C atoms adsorption on the surface W atoms of cluster. the stable adsorption site of CO on the surface of the tungsten clusters locate at the atop position. compared with free CO molecules, the C-O keys become longer after adsorption, proving the CO molecule is activated, but the value of binding energy and adsorption energy account that CO adsorption is dissociated adsorption. Natural bond orbital(NBO) analysis shows that the essence of W atoms interact with CO molecules is the result of the interaction between CO molecules hybrid orbitals and 6s, 5d, 6p and 6d orbitals of W atoms.(2) Based on the ground state structures of Wn CO clusters, the vibrational spectrum, polarizability, the magnetic moment, the rmodynamic properties and orbital level are analyzed. The results show that the IR spectrums of the strongest intensity of clusters which we studied are similar to each other, are assigned to CO stretching mode, and the wavenumber range is between 1752cm-1- 1853.7cm-1. The number of Raman spectra peaks is more than IR spectrum. The strongest peak for raman spectra and IR spectrum of W7 CO cluster is not at the same frequency. Polarization is mainly composed of XX, YY, ZZ direction of component. The total magnetic moment of W7 CO clusters is 4μB which is the maximum one of all clusters. NICS value of all clusters is negative, have shown that these clusters have aromaticity. From the state density analysis we know that d orbitals of clusters has the greatest effect in the electronic structure, and the antibonding orbital is higher than HOMO orbit proving clusters is stable.(3) The structures character, stability and chemical activity of WnCO±(n=7-12) clusters have been studied. Results show that the ion clusters configuration is similar to the ground state structures or metastable structures of neutral clusters, Ion clusters symmetry is reduced, but the spin multiplicity become more. After adsorbed on W cluster, C-O key is activated. The C-O bond length of anionic clusters ground state structure is longer than the corresponding cationic cluster structure, this shows that the anionic clusters have more effects on the dissociation of CO molecules corresponding cationic clusters. The average binding energy of cationic cluster is the largest, the neutral cluster is the second, and the anionic cluster is the least. The infrared spectrogram of Wn CO±(n=7-12) ion clusters ground state configurations is consistent with the neutral clusters, only having a strong peak. Average polarizability tensor of anionic clusters is greater than the corresponding cationic clusters. The magnetic moment of ion clusters is not zero, the spin more severe large clusters, the total magnetic moment are also bigger. The atomic magnetic moment on symmetric position is the same.To sum up, in this paper the author have systematically studied the physical and chemical properties of the ground state of clusters, and revealed the internal relation between microstructure and macro-properties on WnCO0,±(n=7-12) clusters. This article could provide a reliable theoretical basis for experimental research and an appropriate model for developing new catalytic functional materials.