- 學位論文
乙醇分子之量子化學勢能計算與分子動力學模擬
Quantum Chemistry Calculated Intermolecular Interaction and Molecular Dynamics Simulation of Ethanol
摘要
研究主要分量子化學計算與分子動力學模擬兩部分，在量子計算方面，我們使以MP2/aug-cc-pVQZ計算乙醇分子單體之結構最佳化，並以自洽理論(Hartee-Fock, HF)、微擾理論(Møller–Plesset Perturbation Theory, MP)及耦合簇理論(Coupled Cluster Method, CC)等方法對乙醇分子二聚體的分子間作用力進行計算，所有計算均使用Basis Set Supperposition Error(BSSE)修正，其中在HF與MP2方法所搭配的基底為Pople’s medium size與Dunning’s correlation consistent，並對其做最佳化處理，在CCSD(T)則使用aug-cc-pVDZ繪製勢能曲線。接著使用四種方法計算基底極限值(CBS)與MP2計算做比較。我們接著針對選定的19種構型，使用PSI4軟體內的SAPT分析將乙醇分子二聚體間的勢能拆解成四種不同的能量，分別為靜電能、交換能、誘導能與色散能，分析對於不同構型的乙醇分子二聚體，各項吸引力與排斥力對其勢能的影響。 計算完成後，我們使用以原先的OPLS 4-sites model為底，進行修改與新增後得到的9-sites model擬合量子化學計算得到的19種構型的乙醇分子二聚體勢能曲線，架構出力場，並將其代入牛頓方程式去進行分子動力學模擬，接著與實驗值做比較。模擬部分我們沿著汽化曲線從三相點模擬至接近臨界點，得到各溫度下的徑向分佈函數(Radial Distribution Function, RDF)、速度自相關函數(Velocity autocorrelation Function, VAF)、擴散係數(Diffusion coefficient)與黏滯係數(Viscosity)等，與實驗值做比較後皆得到相當不錯的模擬結果，代表以量子化學計算結果架構出的力場進行分子動力學模擬有一定程度的可靠性。
並列摘要
This research including two parts, one is quantum chemical calculation, and another is molecular dynamics simulation. In the first part, we use MP2 with aug-cc-pVQZ to optimize the structure of the ethanol monomer and also calculate the intermolecular interaction potentials of the ethanol-ethanol dimer by using Hartee-Fock self-consistent theory(HF), second-order Møller–Plesset Perturbation Theory(MP2) and Coupled Cluster method(CC), and the correction of the basis-set superposition error(BSSE) has been included. We use MP2 and HF with Pople’s medium size basis sets and Dunning’s correlation consistent basis sets to optimize the ethanol dimer and cauculate the binding energy, and use CCSD(T) only with aug-cc-pVDZ to cauculate. Then we apply four different method to get the complete basis sets limit and compare with the result calculating with MP2. Furthermore, we take the SAPT analysis (Symmetry-Adapted Perturbation Theory) in the PSI4 software to the 19 selected conformers and decompose the potential energy of the ethanol dimer into four different energies, including electrostatic energy, exchange energy, induction energy and dispersion energy. After the calculation is completed, we move to the second part. In this part, we use the 9-sites model, which is modified from OPLS 4-sites model, to fit the ab initio data and construct the force field. Then we substitute it into Newton equation to perform molecular dynamics simulation and compare with the experimental data. We simulate from triple point along the vaporization curve to the critical point, and obtain the data of the Radial Distribution Function(RDF), Velocity autocorrelation Function(VAF), diffusion coefficient and viscosity. The comparison of the simulation and experimental data is acceptable, which represents the molecular dynamics simulation base on the force field constructed by the result of quantum chemical calculation can accurately reproduce the thermodynamic properties.
參考文獻
延伸閱讀
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