Study On Calculation Method Of Free Energy Of Solvent And Methanol Degradation

Thanks to the rapid development of computer technology,molecular dynamics simulation plays an important role in the fields of physics,chemistry and biology also material research.Through the molecular dynamics simulation technology,we can analyze and understand the properties of the system from the micro point of view,which is helpful to verify the correctness of the experiment,and further theoretical calculation can be used to guide experiments.The most common hot research direction is the calculation of free energy of the system in molecular dynamics simulation.The calculation of free energy is important in biological large system because free energy can determine the direction of reaction and also can reflect the difficulty of system combination.Most of the classical calculation methods of free energy need to set some intermediate states and need to perform multiple dynamic simulations,so a lot of calculation resources are consumed.It is urgent to develop a method that can accurately and quickly calculate the free energy of the biology system.In the second chapter of this paper,we calculate the excess free energy of a series of organic pure solvent systems using the new method IE?Interaction Entropy?and the excess interaction enthalpy and excess entropy of the system also are calculated at the same time.Compared the calculation results with the experiment results,it is found that the calculated enthalpy is close to the experimental value,and the entropy is close to the experimental value for the hydrophilic system.But for hydrophobic systems,the difference between enthalpy and experiment is small,and the difference between entropy and experiment is large.Therefore,benzene solvent is selected as an example to research the difference between the computation and the experiment by adjusting the force field parameters of benzene,and we can clearly see that it has a great impact on the results of entropy,and the force field of benzene needs to be further improved to make the theoretical calculation results consistent with the experiment.In the third chapter of this paper,we extend the new IE method to calculate the thermodynamic properties of some alcohol water mixed solutions.In the part of calculation of mixed solutions,we first choose the force field and we find that the OPLS force field is more suitable for the calculation of free energy than the GAFF force field.The calculated value of OPLS force field is closer to the experiment,so we use the OPLS force filed to calculate the mixed solution.Finally,comparing the calculated results with the experimental data,it is found that the results of enthalpy,entropy and free energy of methanol-water and ethanol-water mixtures are not only consistent with the trend of the experimental curve,but also very close to the values.In the fourth chapter,we began to use the quantum chemistry calculation to calculate the methanol degradation mechanism.The main research objects are CH₃OH⁺and CH₃OH⁺⁺degradation mechanism.Through the analysis of the potential energy surface of the two methanol(CH₃OH⁺and CH₃OH⁺⁺)degradation mechanisms,as well as the study of the rate constants of each reaction and the proportion of the final reaction products in the mechanism,we found that the C-O bond in the molecule is more difficult to break than the C-H and O-H bonds,most of the degradation process is hydrogen transfer process,so a large number of H₂,H₂⁺and H₃⁺species are generated.