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Force Field Method And Thermodynamic Properties Prediction

Posted on:2010-11-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:X F LiFull Text:PDF
GTID:1101360302466613Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
Thermodynamic properties data are the key input in chemical engineering processes and unit operations and play fundamental role in experimental research and chemical engineering design. With the rapid advancement of the computer technology and molecular simulation theory, the force field method is regarded as one of the promising method to obtain the thermodynamic data. In this dissertation, we focused on the force field method and conduct an investigation into the prediction of the multiple thermodynamic properties of pure compounds and mixtures based on the first principle force field. The content mainly covers several aspects, which are the establishment of the first principle all-atom TEAM force field method, investigation of the van de Waals (VDW) parameters, development of the alkane and representative polymer force field, comparison of the simulation method and calculation of the various thermodynamic properties.The conclusion can be summarized as follows:1. Development of the novel transferable, extendable, accurate and modularized TEAM force field. The molecular fragment and structured based atom type definition were employed in the TEAM force field to protect the chemical environment around the different atom type as well as to improve the transferability and extendability of the force field parameters. With the well established parameterization process, the general force field with good transferability can reproduce both the gas phase properties as the molecular structure, vibration frequency, rotation barrier and the condensed phase properties as liquid density and heat of vaporization.2. Investigation on the alkane VDW parameters derived from high level ab initio calculation with test particle method. The purpose of this work is to solve the parameter coupling problem and multi-solution problem in the parameter fitting process of the existing force fields. It was found that there are certain relationship between the VDW parameters and the partial charges of different carbon atom types during the VDW optimization process. The VDW parameters of another carbon atom type can be obtained from extrapolation and successfully applied to the simulation.3. The multiple thermodynamic properties of pure alkanes and mixture can be accurate predicted by the ab initio based force field and great improvements were obtained compared with existing force field. These properties include vapor-liquid and critical properties, constant pressure heat capacity, thermal expansivity and isothermal compressibility, transport properties as viscosity, self-diffusion coefficient and thermal conductivity, and liquid density and viscosity of binary mixture. It can be concluded that the molecular simulation method can be an alternative method to obtain the thermodynamic data especially when experimental methods are not available.4. The force fields of two proton exchange membrane polymers were developed based on TEAM force field method and then applied to the liquid-liquid equilibrium calculation of complex mixture systems. We took Nafion-117 as a start point and developed the method to predict the water uptake in the proton exchange membrane polymer. The method was also successfully applied to various polyperfluorosulfonic acid and aromatic proton exchange membrane polymers which means that the method can be generally employed in different polymers. This assessment provides theoretical guidance for optimizing new polymer electrolyte membranes materials.
Keywords/Search Tags:Force Field, Thermodynamic Properties, First Principle, VDW Parameter
PDF Full Text Request
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