Studies On The Mn²⁺-H₂O Systems In Terms Of ABEEM/MM Model And Quantum Chemistry

In this dissertation, firstly a high level quantum chemistry method has been employed to study the hydrated Manganous ionic clusters Mn²⁺(H₂O)_n (n=1¹2). The geometry optimization and vibration frequency have been performed at the B3LYP/6-31++G(d,p) level (the pseudo potential basis set LANL2DZ was employed for Mn²⁺), and the energies have been calculated at the MP2/6-311++G(2d,2p) level with BSSE correction. Results show that: in the hydrated Mn²⁺ clusters, the coordination numbers of Mn²⁺ for the first hydration shell is 6. Compared with the pure bulk water, the OH bond stretching vibration peaks in the solution of Mn²⁺ shifts to the lower wave number, but the vibration frequency of HOH angle does not change much.An accurate Mn²⁺-H2O potential function was constructed based on a next generation polarizable force field, the atom-bond electronegativity equalization fluctuating charge model, ABEEM/MM, and the parameters were determined by fitting the quantum chemistry results. Then the potential function was applied to calculate the structures and binding energies of the Mn²⁺(H₂O)_n (n=1¹2), and the results were in good agreement with those from the quantum chemistry. Furthermore, the structural properties of Mn²⁺ aqueous solution were studied by the ABEEM/MM molecular dynamics simulation, including the radial distribution function (RDF), the angular distribution function (ADF), structures of water, and the charge distribution. The first and second peaks of Mn²⁺-O RDF are located at 2.17(?) and 4.54(?), respectively, and the coordination numbers for the first and second hydration shell integrated from the RDF are 6.77 and 19.94, respectively. The first and second peaks of the O- Mn²⁺-O ADF are located at 80°and 140°, respectively. These results are consistent with those from the experimental measurements and other theoretical simulations. Compared with the ABEEM-7P liquid water, in the Mn²⁺ aqueous solution, the water molecules in the first hydration shell were evidently polarized by Mn²⁺, and the bond lengths of them are stretched, while the bond angle are reduced, which is due to the attraction of metal ions to the oxygen atom and the repulsion of metal ions to the hydrogen atoms. Mn²⁺ does not affect the structures of the second shell water molecules evidently. Analysis on the charge distributions shows that, the charges of water moleculars in the first hydration shell change obviously, and there are evident charge transfer between them with Mn²⁺.