Quantum Chemical Study Of Al_nS₂^±Clusters And Molecular Mechanics Parameters Calculation Of Phosphotungstic Acid

In this paper, we investigate the geometric and electronicproperties of aluminum doped sulphur clusters using quantumchemistry. We calculate the parameters and frequency ofphosphotungstic acid using molecular mechanics. The maincontents are presented as the following:In chapter1, we give a brief introduction to clusters andheteropoly compounds. At first, some basic concepts and generalproperties of clusters have been briefly summered. At second, somemethods in experimental and theoretical studies on clusters areintroduced. At third, some basic concepts and the type ofstructures of heteropoly compounds have been brieflyintroductioned. At last, we have introduced the research meaning ofaluminium doped sulphur clusters and phosphortun-gstic acid.In chapter2, the basic concepts of DFT are introduced.Thomas-Fermi model is the first theory using density of electro-ns as the main variable. Theorem of Hohenberg-Kohn is the fundamentof DFT and is developed to Kohn-Sham method, which can be usedto perform real calculations. Now, new extensions with developedexchang-correlation functionals, which include the local densityapproximation (LDA), generaliz-ed gradient approximation (GGA)and hybrid method, have made DFT more accurate and suitable formore systems. At the end of this chapter, we introduce theGaussian software.In chapter3, the basic concepts of molecular mechanics areintroduced. The force field is the key and core of molecularmechanics. The internal coordinates are used to depict the internalmotion system, which usually has three kinds: bond length, bondangle and dihedral angle. The potential function is used to describeintramolecular or intermolecular bonding. Now, new correction andextension, together with parametrization procedure, which includeinternal coordinates transform, the optimal parameters of the forcefield, united atom theory and frozen internal rotation approximation(FIRA) have made molecular mechanics more accurate and suitablefor more systems. At last, we introduce the JOYCE software.In chapter4, The geometric configurations and electronicproperties of the AlnS2±(n=1-10) clusters are studied using theB3LYP method at6-311G**level. The results show that the structure of AlnS2±(n≤5) clusters plane and solid structures areformed by the combination of two smaller AlmS±(m<n) fragmentsshare with Al atom, while clusters (n>5) cage structures are formedby combing two S atoms and Al clusters. The stability oftree-dimensional structures is ordinary comparing to the linearstructures and planar structures. These AlnS2±clusters with odd nwere more stable than those even n by analyzing the dissociationenergies and the the second-order difference energies.In chapter5, The structure parameters and frequency of sixWells-Dawson type [P2W18O62]6-isomers are studied using the B3LYPmethod at LANL2DZ level. The results obtained with the Gromacsforce field parameters optimization of Hessian matrix. Bycomparing the frequency, we find the frequency range of molecularmechanics method than Gaussian09method111.58cm-1wide,which shows that molecular force field optimization of structure ofheteropoly acid is reliable.