| ThestructuresofX-?H2O?n?X-=F-/Cl-/Br-/I-,n=16?arecalculatedby MP2/6-311++G?2d,2p?//B3LYP/6-311++G?d,p?,in which the pseudo potential basis set Lanl2dz was employed for I-,and the binding energies of stable conformations are calculated at the same level with BSSE correction.The Mulliken charge distributions of the above systems are obtained by HF/STO-3G method.Results show that for the most stable structures of the above systems,the coordination number?CN?of F-is 5 while those of Cl-/Br-/I-are 4.When the CN is between 3 to 5,F-is surrounded by water molecules,while Cl-/Br-/I-are locating on the surface of the water molecules,which indicates the interactions between water molecules are weaker than the interaction between F-and water but stronger than those between Cl-/Br-/I-and water.As the number of water molecule increases gradually,the binding energy increases gradually,the distance between X-and hydrogen atoms of water,RXH increases gradually then tends to be invariant;the absolute value of the charge of X-decreases as a whole,and for the same number of water molecules,the order of the charge transfer magnitude between X-and water is F->Cl->Br->I-.Based on the above results,the ABEEM charge parameters,i.e.,the valence electronegativity X?* and the valence state hardness ??* were refitted and then we constructed a new fluctuating charge potential energy function to describe the interactions between F-/Cl-/Br-and H2O in the sprit of the ABEEMsp/MM model.The related parameters,including a special potential function to treat the hydrogen bond between halide ion and water were determined.Using the constructed potential energy functions,the structures,charge distributions and binding energies of X-?H2O?n?X-=F-/Cl-/Br-,n=16?were studied,and the results are compared with those from the quantum chemistry calculations.The average absolute deviation?AAD?of the binding energy are 3.06,1.96 and 2.05 kcal/mol,and the linear correlation coefficients of binding energies between ABEEMsp/MM model and quantum chemistry method are 0.9705,0.9980,0.9961 for F-,Cl-,and Br-,respectively.The AADs of RXH are 0.019,0.023 and 0.042?,and the AADs of?H-X-H are 1.83°,1.70°and1.51°for F-,Cl-,and Br-,respectively.In terms of charge distribution,the linear correlation coefficients between the results from ABEEMsp/MM and quantum chemistry are 0.9969,0.9910 and 0.9941 for F-,Cl-,and Br-,repectively,and the slopes are between 1.021.26.It can be seen that the results from ABEEM??/MM model have good consistency with those of QM.The preliminary molecular dynamics simulations on the properties of aqueous halide ions has been performed as a further application of the constructed ABEEMsp/MM potential energy functions.For F-,Cl-,and Br-,the first peaks of the radial distribution function?RDF?between X-and oxygen atom of water locate at the RDF 2.76,3.12,and 3.32?,respectively,which are close to the experimental results.The CNs of the first hydration shell are 5.92,6.68,and 6.84,respectively. |
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